JP4696655B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust purification system that performs exhaust purification of an internal combustion engine.

  Since exhaust gas discharged from the internal combustion engine contains particulate matter, a device for collecting particulate matter such as a filter is provided in the exhaust passage so that the particulate matter is not released into the atmosphere. However, as exhaust gas is discharged, particulate matter accumulates on the filter and the back pressure in the exhaust passage increases. Therefore, a technique for oxidizing and removing the particulate matter collected by the filter by increasing the exhaust temperature is widely used.

In addition, a technique for generating plasma in an exhaust passage of an internal combustion engine to oxidize and remove particulate matter in the exhaust gas discharged has been disclosed (see, for example, Patent Document 1). In this technology, a plurality of nitrogen dioxides and a plurality of ozone are generated in the exhaust gas by generating plasma in the exhaust gas containing the particulate matter, and the particulate matter in the exhaust gas is utilized by utilizing these oxidation capabilities. Is removed by oxidation.
JP 2004-169643 A JP 2003-343237 A

  In order to oxidize and remove particulate matter contained in the exhaust discharged from the internal combustion engine, it is useful to supply a peroxide such as ozone into the exhaust. However, this peroxidant not only exhibits its own oxidizing ability to particulate matter, but also exhibits oxidizing ability to various substances (oxidized substances) in the exhaust. For example, since exhaust gas contains nitrogen monoxide, hydrocarbons, carbon monoxide, etc., even if a peroxide is supplied to the exhaust gas, these substances are preferentially oxidized over particulate matter, Oxidation of particulate matter by oxidant is not performed well.

  In addition, even if a peroxide such as ozone is generated in the exhaust gas by plasma, ozone may be sufficiently present in the vicinity of the region where the plasma is generated. Since the above-described oxidizable substance is oxidized, the particulate matter is not oxidized with ozone.

  In view of the above problems, an object of the present invention is to provide an exhaust purification system that better oxidizes and removes particulate matter contained in exhaust gas using a peroxide.

  In the present invention, in order to solve the above-described problem, among the particulate matter collected by the particulate matter collecting device, the particulate matter is generated outside the exhaust passage of the internal combustion engine, particularly in a place where the particulate matter is easily deposited. It was decided to supply the peroxidant directly.

  More specifically, the present invention relates to an exhaust gas purification system for an internal combustion engine, an exhaust passage through which exhaust gas discharged from the internal combustion engine flows, and a particulate shape that is provided in the exhaust passage and collects particulate matter in the exhaust gas. When the temperature of the exhaust gas flowing into the particulate matter collection device is less than or equal to a predetermined temperature, the peroxide collection device, a peroxide generation device that produces a peroxide outside the exhaust passage, And a peroxidant supply means for supplying the peroxidant generated by the generator to a predetermined site where the particulate matter is deposited in the particulate matter trapping device.

  In the exhaust gas purification system for an internal combustion engine described above, the particulate matter in the exhaust is collected by the particulate matter collecting device, and the release to the atmosphere is suppressed. Here, part of the particulate matter collected by the particulate matter collection device is oxidized and removed by exposure to a high exhaust temperature. However, the collected particulate matter is not oxidized at the exhaust temperature and gradually accumulates at the predetermined portion such as a low temperature portion in the particulate matter collecting device. Therefore, in the particulate matter collecting apparatus according to the present invention, the peroxide agent is directly supplied to the predetermined portion where the particulate matter is easily deposited by the peroxide supply means, thereby oxidizing the particulate matter. Remove more reliably and efficiently.

  Here, the peroxide generator generates the peroxide outside the exhaust passage. This is because when the peroxidant is generated in the exhaust passage, it reacts with nitrogen monoxide, hydrocarbons, carbon monoxide, etc. in the exhaust, and most of the generated peroxidant disappears before oxidizing the particulate matter. Because it will end up.

  Further, the supply of the peroxide by the peroxide supply means is performed when the exhaust temperature is equal to or lower than the predetermined temperature. The oxidizing agent may lose its oxidizing ability depending on the temperature of the atmosphere in which it is placed. Generally, when the temperature of the atmosphere rises excessively, the oxidizing ability of the peroxidant is lost. Therefore, the supply of the peroxide by the peroxide supply means is performed when the exhaust gas temperature is at a temperature at which the oxidizing ability of the peroxide to be supplied is maintained, that is, when the temperature is below the predetermined temperature. In addition, ozone etc. are mentioned as a peroxide agent.

  Thus, in the exhaust gas purification system for an internal combustion engine according to the present invention, in order to supply the peroxidant to the place where the particulate matter is deposited while maintaining the oxidizing ability of the peroxidant, It becomes possible to oxidize and remove better.

  Here, in the exhaust gas purification system for an internal combustion engine described above, it may be an outer peripheral portion of an exhaust inflow surface of the particulate matter trapping device. The outer periphery of the exhaust gas inflow surface of the particulate matter collection device has a higher heat dissipation to the outside of the particulate matter collection device in addition to the removal of heat due to the exhaust flow, so the temperature is higher than other places. Tend to be lower. For this reason, particulate matter is likely to deposit on the outer peripheral portion, and is one of the parts that need to be oxidized and removed by a peroxide.

  Further, when the particulate matter collecting device is a filter that collects particulate matter in the exhaust gas, the predetermined part may be a peroxidant passage provided inside the base material of the filter. Good. When particulate matter in the exhaust gas is collected by the filter, the particulate matter is deposited around the filter substrate. Therefore, the peroxide generated by the peroxide generator is supplied to the peroxide passage provided inside the substrate. Then, the peroxidant flowing through the passage oozes out to the filter base material, and the particulate matter deposited on the base material can be oxidized and removed more efficiently.

  Further, in the exhaust gas purification system for an internal combustion engine, the peroxidant supply means supplies the peroxidant to the plurality of predetermined portions along the flow of exhaust gas of the particulate matter trapping device, and further on the downstream side. The amount of peroxide supplied to the predetermined part may be reduced as the process goes to step (b). A part of the peroxidant supplied to the predetermined upstream site flows downstream without reacting with the particulate matter. In anticipation of the amount of peroxidant flowing into the downstream side, by reducing the amount of peroxidant supplied to the predetermined site on the downstream side, it becomes possible to provide an appropriate amount of peroxidant for the oxidation removal of the particulate matter. . Further, it is possible to reduce the amount of the peroxide agent that passes through the particulate matter collecting device and leaks to the outside.

Here, in the exhaust gas purification system for an internal combustion engine up to the above, in the case where it further includes a determination unit that determines the accumulation state of the particulate matter in the predetermined part, the particulate matter is more than a predetermined amount in the predetermined part by the determination unit. When it is determined that it is deposited, the peroxide agent may be supplied to the predetermined portion by the peroxide agent supply means.

  That is, if the peroxide agent is always supplied by the peroxide agent supply means, the peroxide agent may be supplied even when it is unnecessary, leading to useless consumption of the peroxide agent. Therefore, only when it is determined by the determination means that a predetermined amount or more of the particulate matter is deposited at the predetermined site, that is, when it is determined that the deposited particulate matter needs to be oxidized and removed. By supplying the peroxide, it is possible to avoid unnecessary consumption of the peroxide. This predetermined amount may be determined in accordance with the particulate matter collection ability of the particulate matter collection device.

  In an exhaust gas purification system for an internal combustion engine, it becomes possible to better oxidize and remove particulate matter contained in the exhaust gas using a peroxide.

  Now, an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust purification system according to the present invention is applied and its control system. The internal combustion engine 1 is a compression ignition type internal combustion engine having four cylinders 2. Further, a fuel injection valve 3 for directly injecting fuel into the combustion chamber of the cylinder 2 is provided. The fuel injection valve 3 is connected to a pressure accumulating chamber 4 that stores fuel pressurized to a predetermined pressure. An intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 is connected to a combustion chamber via an intake port. Similarly, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 is connected to a combustion chamber via an exhaust port. Here, the intake port and the exhaust port are provided with an intake valve and an exhaust valve, respectively.

  The intake branch pipe 7 is connected to the intake pipe 8. An air flow meter 9 for detecting the amount of intake air flowing through the intake pipe 8 is provided upstream of the intake pipe 8, and an intake throttle valve 10 for adjusting the flow rate of intake air flowing through the intake pipe 8 is provided further downstream thereof. It has been. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10.

  An intake pipe 8 upstream of the intake throttle valve 10 is provided with a compressor side of a supercharger 16 that operates using exhaust energy as a drive source, and an exhaust branch pipe 12 is provided with a turbine side of the supercharger 16. . The supercharger 16 is a so-called variable capacity supercharger. The supercharger 16 has a movable nozzle vane therein, and the supercharging pressure by the supercharger 16 is controlled by adjusting the opening degree of the nozzle vane. . An intercooler 15 is provided in the intake pipe 8 downstream of the supercharger 16 and upstream of the intake throttle valve 10 for cooling the intake air that has been pressurized by the supercharger 16 and has reached a high temperature. .

  Further, the turbine side of the supercharger 16 is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected to a muffler downstream. A device for purifying exhaust gas is provided in the middle of the exhaust pipe 13. This exhaust purification device is composed of a monolithic catalyst 18 having oxidation ability and a filter 14 located on the downstream side thereof. The filter 14 has the ability to collect particulate matter (hereinafter also referred to as “PM”) in the exhaust gas, and the filter has a so-called NOx storage reduction catalyst (hereinafter referred to as “NOx catalyst”). Is carried.

The exhaust branch pipe 12 upstream of the supercharger 16 is provided with a fuel addition valve 17 for adding fuel to the exhaust. Further, the internal combustion engine 1 is provided with an EGR device 21. The EGR device 21 recirculates a part of the exhaust gas flowing through the exhaust branch pipe 12 to the intake branch pipe 7. The EGR device 21 includes an EGR passage 22 extending from the exhaust branch pipe 12 (upstream side) to the intake branch pipe 7 (downstream side), and an EGR for cooling EGR gas provided in order from the upstream side on the EGR passage 22. A cooler 23 and an EGR valve 24 for adjusting the flow rate of EGR gas are included.

  The internal combustion engine 1 is also provided with an electronic control unit (hereinafter referred to as “ECU”) 20 for controlling the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, and the like for storing various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  Here, the fuel injection valve 3 performs an opening / closing operation by a control signal from the ECU 20. That is, according to a command from the ECU 20, the fuel injection timing and the fuel injection amount from the fuel injection valve 3 are controlled for each injection valve in accordance with the operation state such as the engine load and engine speed of the internal combustion engine 1. The fuel addition valve 17 is also controlled in accordance with a command from the ECU 20.

  Further, an accelerator opening sensor 31 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the accelerator opening and calculates an engine load required for the internal combustion engine 1 based on the signal. A crank position sensor 30 is electrically connected to the ECU 20, and the ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1, and the engine rotational speed of the internal combustion engine 1 and the piston position in each cylinder 2. Etc. are detected. Further, a temperature sensor 32 for detecting the temperature of the exhaust gas flowing into the monolith catalyst 18 is provided in the exhaust pipe 13 upstream of the monolith catalyst 18, and further, the exhaust pipe 13 between the monolith catalyst 18 and the filter 14 is provided in the exhaust pipe 13. A temperature sensor 33 for detecting the temperature of the exhaust gas flowing into the filter 14 is provided, and these temperature sensors are electrically connected to the ECU 20.

  In the internal combustion engine 1 configured as described above, exhaust purification is performed by the monolith catalyst 18 and the filter 14. In particular, the purification of PM contained in the exhaust will be described below. The PM in the exhaust gas is collected by the filter 14, so that release to the outside is suppressed. However, when the amount of trapping gradually increases, the back pressure in the exhaust passage 13 increases and the engine load of the internal combustion engine 1 increases. Therefore, when the amount of PM collected by the filter 14 exceeds a certain amount, the collected PM is oxidized and removed. The collected PM amount is detected and estimated based on the exhaust pressure difference before and after the filter, the fuel consumption, the operation history of the internal combustion engine 1, and the like.

  Here, when the exhaust gas temperature is relatively high, for example, when the engine load of the internal combustion engine 1 is a medium load or a high load, fuel is added from the fuel addition valve 17 to the exhaust gas in accordance with a command from the ECU 20. The fuel added to the exhaust is oxidized by the monolith catalyst 18 to further increase the exhaust temperature. Then, the PM collected by the filter 17 is oxidized and removed with the increased thermal energy of the exhaust gas.

  However, even if fuel is added from the fuel addition valve 17, there is a place in the filter 14 where the temperature does not rise sufficiently. That is, in places where the heat of the filter is taken away by the flow of exhaust or where heat is radiated to the outside of the filter, the temperature of the filter cannot be raised sufficiently, and the collected PM is gradually not oxidized and removed. Accumulate. For example, PM is easily deposited on the exhaust inflow surface of the filter 14 because the temperature rise is relatively small. Further, PM may be accumulated in the filter 14.

Therefore, the exhaust purification system of the internal combustion engine 1 according to the present invention is provided with a device for oxidizing and removing PM deposited on the filter 14. This apparatus mainly includes an ozone generator 40, an air pump 41, an ozone pipe 42, and valves 43, 44, and 45. In accordance with a command from the ECU 20, plasma is generated by the ozone generator 40 with respect to the air sent by the air pump 41 to generate ozone as a peroxidant. The ozone generator 40 is installed outside the exhaust pipe 13 of the internal combustion engine 1. And the produced | generated ozone is supplied to the predetermined | prescribed location of the apparatus which performs exhaust gas purification along the piping 42 for ozone.

  First, the supply destination of the first ozone is upstream of the monolith catalyst 18. This supply of ozone is performed by opening and closing the valve 43. The ozone supplied by opening the valve 43 mainly oxidizes and removes PM deposited inside the monolith catalyst 18.

  The second ozone supply destination is the outer peripheral portion of the exhaust inflow surface of the filter 14. Here, the supply of ozone at the outer peripheral portion of the exhaust inflow surface of the filter 14 will be described with reference to FIG. 2A is a view of the filter 14 as viewed from the exhaust inflow surface, and FIG. 2B is a cross-sectional view in the lateral direction. The filter 14 has a wall flow type structure, and its end faces are alternately plugged. In FIG. 2 (a), it means a portion where the black squares are plugged, and means a portion where the white squares are not plugged.

  Here, an annular pipe 42 a is provided on the outer peripheral portion of the exhaust inflow surface of the filter 14. The annular pipe 42 a is connected to the ozone pipe 42, and ozone generated by the ozone generator 40 is supplied thereto by opening and closing the valve 44. The supplied ozone falls on the outer peripheral portion of the exhaust inflow surface of the filter 14 as shown in FIG. As a result, it is possible to oxidize and remove the PM deposited on the outer peripheral portion of the exhaust inflow surface of the filter 14 that has a large amount of heat radiation to the outside and easily accumulates PM with ozone having a strong oxidizing power. At this time, ozone is supplied to the PM directly in a place where it is easily deposited. Therefore, ozone is oxidized by a substance that is easily oxidized by ozone present in the exhaust gas, such as nitrogen monoxide, carbon monoxide, hydrocarbons, and the like. The possibility of consumption is reduced, and more efficient PM oxidation removal is possible.

  The third ozone supply destination is inside the base material of the filter 14. Here, based on FIG. 3, the supply of ozone inside the base material of the filter 14 will be described. 3A is a cross-sectional view when the filter 14 is cut in the horizontal direction, and FIG. 3B is a cross-sectional view in the horizontal direction. The filter 14 has a base material that is the basis of the structure. In this embodiment, an ozone pipe 42 is connected to a passage 42b provided inside the base material, and ozone generated by the ozone generator 40 is supplied by opening and closing the valve 45. The supplied ozone is transmitted to the inside of the filter 14 through the passage 42b as shown in FIG. Then, ozone leaks out from the passage 42b into the hole of the filter 14, and the PM accumulated in the filter 14 can be oxidized and removed with ozone having a strong oxidizing power. At this time, since the supply of ozone to the PM is performed directly inside the filter 14, the PM can be oxidized and removed more efficiently as in the case of the second ozone supply described above.

  Here, PM oxidation removal control performed in the internal combustion engine 1 will be described based on FIG. 4 based on the above-described PM oxidation removal by supplying ozone to the filter 14. Note that the PM oxidation removal control in this embodiment is a routine that is repeatedly executed by the ECU 20 at a constant cycle.

In S101, it is determined whether or not PM has accumulated on the filter 14 to such an extent that the PM affects the back pressure of the exhaust pipe 13. For example, when the PM collected by the filter 14 due to the fuel addition to the exhaust gas by the fuel addition valve 17 is oxidized and removed, as described above, the portion such as the outer peripheral portion of the exhaust inflow surface where PM is likely to accumulate gradually PM accumulates. Therefore, it is determined that a relatively large amount of PM accumulates on the filter 14 and affects the back pressure of the exhaust pipe 13 when the fuel addition by the fuel addition valve 17 is executed a predetermined number of times. In addition to this, the degree of PM accumulation in the filter 14 may be estimated based on the operating state history of the internal combustion engine 1 or the like. If it is determined that PM has accumulated on the filter 14 to such an extent that the PM affects the back pressure of the exhaust pipe 13, the process proceeds to S102, and if a negative determination is made, this control is terminated.

  In S102, it is determined based on the detection values of the temperature sensor 32 and the temperature sensor 33 whether the exhaust temperature is equal to or lower than a predetermined temperature T1. The predetermined temperature T1 is an exhaust temperature at which the oxidizing ability of ozone as a peroxidant can be maintained. If the exhaust temperature is excessively high, ozone decomposes and its oxidizing ability disappears. Therefore, only when the exhaust gas temperature is equal to or lower than the predetermined temperature T1, ozone is supplied and oxidation removal of PM is executed. Here, the exhaust gas temperature detected by the temperature sensor 32 is a criterion for determining whether or not to oxidize and remove PM deposited on the monolith catalyst 18 by opening the valve 43. Further, the exhaust gas temperature detected by the temperature sensor 33 is a criterion for determining whether or not to remove oxidized PM deposited on the filter 14 by opening the valve 44 and the valve 45. When the exhaust temperature is lower than the predetermined temperature, the process proceeds to S103, and when the exhaust temperature is not lower than the predetermined temperature, this control is finished.

  In S103, the valve 43 and the valve 44 are opened, and supply of ozone to the outer peripheral portion of the monolith catalyst 18 and the exhaust inflow surface of the filter 14 is started. Thereby, the oxidation removal of PM deposited in the corresponding place is more efficiently performed by ozone having strong oxidizing power. When the process of S103 ends, the process proceeds to S104.

  In S104, the valve 45 is opened to supply ozone to the passage 42b inside the filter 14 substrate. Here, as shown in FIG. 3B, there are three types of supply ports for supplying ozone into the base material of the filter 14: an upstream supply port 42c, an intermediate supply port 42d, and a downstream supply port 42e. Each is for supplying ozone uniformly into the base material of the filter 14. Then, the supplied ozone oxidizes and removes PM accumulated in the filter 14.

  Here, when ozone is supplied from these supply ports, the supply amount of ozone is decreased in the order of the upstream supply port 42c, the intermediate supply port 42d, and the downstream supply port 42e. This is because part of the ozone supplied from the upstream supply port 42c and the intermediate supply port 42d rides on the exhaust flow and flows downstream, and oxidizes and removes PM located on the downstream side. Therefore, even if the amount of ozone supplied to the supply port located on the downstream side is reduced, PM can be satisfactorily removed by oxidation, and the amount of ozone consumed can be suppressed. After the process of S104, this control is terminated.

  According to this control, PM contained in the exhaust gas is collected by the filter 14, and PM deposited on the filter 14 can be satisfactorily oxidized and removed.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas purification system for an internal combustion engine according to an embodiment of the present invention is applied and a control system thereof. It is a 1st figure which shows supply of the ozone to the filter in the exhaust gas purification system of the internal combustion engine which concerns on the Example of this invention. It is a 2nd figure which shows supply of the ozone to the filter in the exhaust gas purification system of the internal combustion engine which concerns on the Example of this invention. It is a flowchart regarding the control for the oxidation removal of the particulate matter performed in the exhaust gas purification system of the internal combustion engine according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Fuel injection valve 14 ... Filter 17 ... Fuel addition valve 18 ... Monolith catalyst 12 ... Exhaust branch pipe 14 ... Storage Reduced NOx catalyst (NOx catalyst)
17 ... Fuel addition valve 20 ... ECU
32 ... Temperature sensor 40 ... Ozone generator 42 ... Ozone piping 42a ... Annular piping 42b ... Passage 42c ... Upstream supply port 42d ... Intermediate supply port 42e ... Downstream supply port

Claims (3)

An exhaust passage through which exhaust discharged from the internal combustion engine flows;
A particulate matter collecting device that is provided in the exhaust passage and collects particulate matter in the exhaust;
A peroxide generator for generating a peroxide outside the exhaust passage;
When the temperature of the exhaust gas flowing into the particulate matter collecting device is equal to or lower than a predetermined temperature, the particulate matter is deposited in the particulate matter collecting device by the peroxide produced by the peroxide producing device. A peroxide supply means for supplying to a predetermined site;
With
The exhaust gas purification system for an internal combustion engine, wherein the predetermined portion is an outer peripheral portion of an exhaust inflow surface of the particulate matter trapping device . An exhaust passage through which exhaust discharged from the internal combustion engine flows;
A particulate matter collecting device that is provided in the exhaust passage and collects particulate matter in the exhaust;
A peroxide generator for generating a peroxide outside the exhaust passage;
When the temperature of the exhaust gas flowing into the particulate matter collecting device is equal to or lower than a predetermined temperature, the particulate matter is deposited in the particulate matter collecting device by the peroxide produced by the peroxide producing device. A peroxide supply means for supplying to a predetermined site;
With
The particulate matter collection device is a filter that collects particulate matter in the exhaust,
The exhaust gas purification system for an internal combustion engine, wherein the predetermined part is a passage for a peroxide agent provided in a base material of the filter. An exhaust passage through which exhaust discharged from the internal combustion engine flows;
A particulate matter collecting device that is provided in the exhaust passage and collects particulate matter in the exhaust;
A peroxide generator for generating a peroxide outside the exhaust passage;
When the temperature of the exhaust gas flowing into the particulate matter collecting device is equal to or lower than a predetermined temperature, the particulate matter is deposited in the particulate matter collecting device by the peroxide produced by the peroxide producing device. A peroxide supply means for supplying to a predetermined site;
With
The peroxidant supply means supplies the peroxidant to the plurality of predetermined sites along the flow of exhaust gas from the particulate matter collection device, and supplies the peroxygen to the predetermined sites as going downstream.
An exhaust purification system for an internal combustion engine, characterized in that the amount of the agent is reduced.

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