JP2010196569A - Exhaust emission control system and exhaust emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system, which includes an exhaust emission control device in an exhaust passage of an internal combustion engine and supplies fuel to the exhaust emission control device as required, and an exhaust emission control method which allows a rise in temperature of a catalyst in the exhaust emission control device by efficiently supplying secondary air to an exhaust passage at desulfurization treatment and PM regeneration treatment after an engine starts. <P>SOLUTION: In an exhaust emission control device 18 in an exhaust passage 11 of an internal combustion engine 10, air A1 not pressurized and air A2 pressurized by a compressor of a supercharger are selectively supplied to an exhaust passage through the medium of a lead valve 32. When an engine starts, air A1 not pressurized is intermittently supplied to the exhaust emission control device 18 in response to pulsation of exhaust pressure so that oxidation reaction of the fuel in a catalyst is promoted. In desulfurization treatment and PM regeneration treatment, pressurized air A2 is supplied to the exhaust emission control device 18 at a sufficient flow rate to oxidize an abundance of fuel, thereby time of raising temperature is shortened. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device such as a NOx occlusion reduction type catalyst or a diesel particulate filter (DPF) in the exhaust passage during warm-up immediately after engine start-up, during desulfurization processing, or during PM regeneration processing. The present invention relates to an exhaust gas purification system and an exhaust gas purification method for supplying fuel and secondary air.

  In order to purify the exhaust gas of an internal combustion engine mounted on an automobile or the like using light oil or gasoline as fuel, an exhaust gas purification device (post-treatment device) is provided in the exhaust passage of the internal combustion engine to purify the exhaust gas. As this exhaust gas purification device, an oxidation catalyst (DOC) such as a three-way catalyst, a NOx storage reduction catalyst (LNT), a diesel particulate filter (DPF), a DPF with catalyst (CSF), or the like is used.

An oxidation catalyst such as a three-way catalyst oxidizes unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) by catalytic action. NOx occlusion reduction type catalyst carries alkali or alkaline earth metal together with noble metal, and the exhaust gas air-fuel ratio is lean and oxidizes nitric oxide (NO) to nitrogen dioxide (NO ₂ ), which is then nitrated on the catalyst. It adsorbs and purifies NOx, releases the adsorbed NOx when the air-fuel ratio of the exhaust gas is rich, and reduces the released NOx.

  The DPF with catalyst collects PM when the exhaust gas temperature or the catalyst temperature is equal to or lower than the PM combustion start temperature, purifies the exhaust gas, and PM burns the DPF with catalyst when the collected PM accumulates to some extent. The temperature is raised above the start temperature and the combustion is removed, thereby purifying the exhaust gas.

  The catalysts of these exhaust gas purification apparatuses do not exhibit their catalytic action at low temperatures, but do exhibit their catalytic action in the activation temperature range above the activation temperature. Therefore, when the engine is started, the catalyst temperature is low, and until the activation temperature is reached, CO, HC, NOx, etc. in the exhaust gas are not purified by the catalyst but flow out downstream of the exhaust gas purification device, It will make the environment worse. Therefore, when the engine is started, in order to raise the temperature of the catalyst in a short time, the fuel supplied to the upstream side of the catalyst is oxidized on the catalyst, and the catalyst is heated by the reaction heat generated at this time.

  In this regard, rich components in the exhaust gas are contained in the exhaust gas passage upstream of the catalyst when the catalyst is warmed up, and when the catalyst is in an inactive state and the catalyst needs to be warmed up. The combustion of the internal combustion engine is controlled so as to reach a temperature at which afterburning is possible, and at the same time, secondary air is introduced into the exhaust gas passage upstream of the catalyst, and afterburning is naturally generated in the exhaust pipe. A control device for an internal combustion engine that warms up a catalyst early with combustion heat has been proposed (see, for example, Patent Document 1).

  However, it is necessary to raise the DPF to a relatively high temperature of about 700 ° C. in the NOx storage reduction catalyst for desulfurization processing in the NOx storage reduction catalyst and about 700 ° C. for PM regeneration processing in the DPF with catalyst, not only at the time of engine start. There is.

  That is, in the NOx occlusion reduction type catalyst, a sulfur component is contained in the fuel of the internal combustion engine, and this sulfur component is adsorbed on the catalyst as a sulfate, so that the NOx occlusion capacity of the NOx occlusion material decreases. There is a problem of sulfur poisoning. In order to regenerate the NOx storage material from this sulfur poisoning, the temperature of the catalyst is raised to about 700 ° C., and while maintaining this temperature, a state in which oxygen is insufficient with respect to the amount of fuel contained in the exhaust gas is created. NOx storage material is desulfurized.

  Also, in the DPF device for collecting PM, a DPF with a catalyst that supports an oxidation catalyst or a PM oxidation catalyst and lowers the combustion start temperature of the PM collected by the DPF is used. Even in the DPF, when the amount of PM collected to avoid an increase in exhaust pressure due to clogging has increased to some extent, the temperature of the DPF with catalyst is raised to about 550 ° C. by collecting the exhaust gas, and the collected PM PM regeneration processing is performed to remove the combustion.

  In this desulfurization process and PM regeneration process, in order to raise the catalyst temperature in a short time, the engine speed is not as low as the idling speed immediately after the engine is started. There is a problem that the supply amount is insufficient. For this reason, it is conceivable to provide a pump for supplying secondary air. However, in that case, there is a problem that a pump for supplying air is required.

  In other words, if a relatively large amount of fuel is supplied to the exhaust gas purification device and an amount of secondary air corresponding to that amount is introduced, even if a relatively large amount of fuel is supplied to the exhaust gas purification device, the reaction will not occur. If no suitable air (or oxygen) is introduced, unburned fuel will be generated, and as a result, the calorific value will not increase as expected. Further, even if fuel is supplied in excess of the amount of air (or the amount of oxygen) introduced by the negative pressure due to exhaust pulsation, the remaining amount of air will remain unburned. That is, the amount of fuel supplied limited by the amount of air introduced under negative pressure does not match the amount of heating of the catalyst in a short time.

JP 2001-263050 A

  The present invention has been made in view of the above situation, and an object of the present invention is to provide an exhaust gas purifying device for an exhaust passage of an internal combustion engine, and, if necessary, the exhaust by post injection or direct combustion injection in an exhaust pipe. In the exhaust gas purification system that supplies fuel to the gas purification device, the secondary air is supplied to the exhaust passage of the internal combustion engine to raise the temperature of the catalyst of the exhaust gas purification device. Efficient temperature rise by intermittently sucking atmospheric air using exhaust pulsation and supplying exhaust gas with high oxygen concentration and exhaust gas with high fuel concentration to the catalyst alternately in time Furthermore, in the supply of secondary air during desulfurization treatment and PM regeneration treatment, a sufficient amount of air can be introduced by introducing air pressurized by the compressor against the amount of fuel supplied in large quantities in the exhaust passage. Supplying To provide a faster exhaust gas purification system can warm and exhaust gas purification method.

  In order to achieve the above object, an exhaust gas purification system of the present invention includes an exhaust gas purification device for an exhaust passage of an internal combustion engine and, if necessary, the exhaust gas purification device by post injection or direct combustion injection in an exhaust pipe. In the exhaust gas purification system for supplying fuel to the exhaust gas, the first air supply pipe for supplying secondary air that supplies the air in the intake passage upstream of the compressor of the supercharger or the air in the passage communicating with the atmosphere to the exhaust port And a second air supply pipe for supplying secondary air for supplying air in the intake passage downstream of the compressor to the exhaust port, and a first air control valve in the first air supply pipe, A second air control valve is provided in each of the second air supply pipes, and further, the flow of air to the exhaust port side is permitted, but the flow of exhaust gas from the exhaust port is blocked. A control device configured by providing a check valve and controlling the fuel supply to the exhaust gas purification device and the opening and closing of the first air control valve and the second air control valve is configured to perform the exhaust by post-injection when the engine is started. While supplying fuel to the gas purification device, the first air flow control valve is opened and the second air control valve is closed, and the air amount is controlled by the first air control valve, and air is supplied to the exhaust port. At the time of desulfurization treatment for removing sulfur components accumulated in the catalyst of the exhaust gas purification device to be supplied, or at the time of PM regeneration treatment for removing particulate matter accumulated in the exhaust gas purification device by combustion, post injection or exhaust The fuel is supplied to the exhaust gas purification device by direct injection in the pipe, and the first air control valve is closed and the second air control valve is opened to control the supply of air to the exhaust port. It is formed.

  In addition, an exhaust gas purification method of the present invention for achieving the above object includes an exhaust gas purification device for an exhaust passage of an internal combustion engine, and, if necessary, the exhaust gas by post injection or direct combustion injection in an exhaust pipe. A first air supply pipe for supplying secondary air for supplying fuel to the purifier and further supplying air in the intake passage upstream of the compressor of the supercharger or air in the passage communicating with the atmosphere to the exhaust port; A second air supply pipe for supplying secondary air for supplying air in the intake passage downstream of the compressor to the exhaust port, and a first air control valve in the first air supply pipe, A second air control valve is provided in each of the second air supply pipes, and a check valve is provided to prevent the flow of the exhaust gas from the exhaust port while allowing the flow of air to the exhaust port side. The In the exhaust gas purification method of the exhaust gas purification system, when starting the engine, fuel is supplied to the exhaust gas purification device by post-injection, and the first air flow control valve is opened and the second air control valve is closed. In the desulfurization process for supplying air to the exhaust port while removing the sulfur component accumulated in the catalyst of the exhaust gas purification device while controlling the amount of air with the first air control valve, or for the exhaust gas purification At the time of PM regeneration processing in which particulate matter accumulated in the apparatus is removed by combustion, fuel is supplied to the exhaust gas purification apparatus by post injection or direct injection in the exhaust pipe, and the first air control valve is closed and the second air is closed. A control valve is opened to supply air to the exhaust port.

  According to the exhaust gas purification system and the exhaust gas purification method of the present invention, when the engine speed at the start of the internal combustion engine is relatively low, the secondary air is intermittently used by utilizing the pulsation of the exhaust pressure at the exhaust port. Since the exhaust gas is supplied to the exhaust gas purification device, the composition of the exhaust gas flowing into the exhaust gas purification device alternates in time between when the oxygen concentration is high and when the fuel concentration is high. By flowing into the exhaust gas purification device in a state separated from the fuel concentration gas, oxygen can be adsorbed on the catalyst as oxygen atoms having high reaction activity, and the combustion reaction on the catalyst can be performed. It can be significantly promoted.

  In addition, when the exhaust gas purifying device requires a temperature higher than the normal catalyst temperature, the exhaust gas is supplied with the air pressurized by the compressor of the supercharger during the desulfurization process or the PM regeneration process. The amount of air that can sufficiently oxidize the fuel that has been supplied in large quantities to the purification device can be supplied. Therefore, the temperature of the exhaust gas and the exhaust gas purification device can be raised with a large amount of heat generated by the oxidation of the fuel without causing the oxidation reaction to stop due to lack of oxygen, so that the temperature raising time can be shortened. Accordingly, in the temperature raising and heating process of the catalyst of the exhaust gas purification device, a large amount of fuel can be supplied to the exhaust gas purification device to quickly increase the catalyst temperature, and deterioration of fuel consumption can be suppressed.

  In addition, air that has been boosted to the boost pressure required for the torque generated by the internal combustion engine is introduced into the exhaust port during desulfurization processing and PM regeneration processing of the exhaust gas purification device. In this case, a sufficient amount of air (oxygen) can be secured without being influenced by exhaust pulsation, and the exhaust gas purification device can be heated to a temperature capable of desulfurization or a temperature capable of regenerating PM, and the temperature can be maintained. It becomes like this.

It is the figure which showed the structure of the exhaust-gas purification system of embodiment of this invention. It is the figure which showed the structure of the 1st air supply piping and 2nd air supply piping for secondary air supply. It is the figure which showed the open state of the non-return valve when attracting | sucking air of atmospheric pressure. It is the figure which showed the closed state of the check valve. It is the figure which showed the open state of the non-return valve when supplying the air after pressure | voltage rising by the compressor. It is the figure which showed an example of the control flow of the secondary air supply at the time of engine starting. It is the figure which showed an example of the control flow of the secondary air supply at the time of a desulfurization process or PM regeneration process.

  Hereinafter, an exhaust gas purification system and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings. 1 to 5 show a configuration of an exhaust gas purification system 1 according to an embodiment of the present invention.

  The engine 10 of the exhaust gas purification system 1 includes an intake intake air amount sensor 12 (MAF sensor), a turbocharger (supercharger) 13 compressor 13a, an intercooler 14 and an intake valve in an intake passage 11 connected to an intake manifold 10a. (Intake throttle) 15 is provided. Further, the turbine 13b of the turbocharger 13, the direct fuel supply device (exhaust pipe injector) 17 for injecting fuel directly into the exhaust passage 16 and the exhaust gas purification are connected to the exhaust passage 16 connected to the exhaust manifold 10b. An apparatus (post-processing apparatus) 18 is provided. Further, an EGR cooler 20 and an EGR valve 21 are provided in the EGR passage 19 that connects the exhaust manifold 10b and the intake manifold 10a and through which the EGR gas Ge passes.

  In the configuration of FIG. 1, the exhaust gas purification device 18 includes an oxidation catalyst device (DOC) 18a, a NOx occlusion reduction type catalyst device (LNT) 18b, and a filter device with catalyst (CSF) 18c.

  The oxidation catalyst device 18a is formed by supporting an oxidation catalyst such as platinum on a porous ceramic honeycomb structure support. This oxidation catalyst has the role of purifying exhaust gas by oxidizing HC and CO in the exhaust gas, NOx regeneration for recovering the NOx storage capacity of the NOx storage reduction catalyst 3, and recovery from sulfur poisoning. Therefore, during the desulfurization process or the PM regeneration process of the catalyst-equipped filter 18c, the temperature of the exhaust gas G is raised by oxidizing a part of the fuel supplied into the exhaust passage 16. Yes.

  The NOx occlusion reduction type catalyst device 18b is formed by supporting an alkali metal or an alkaline earth metal together with a noble metal, and oxidizes NO in exhaust gas containing excess oxygen and adsorbs it as a nitrate on the catalyst to purify NOx. . The NOx occlusion reduction type catalyst stores NOx when the exhaust gas is lean, and releases the stored NOx when the exhaust gas is rich, and reduces the released NOx in a reducing atmosphere to reduce NOx. To reduce. In this rich air-fuel ratio control for NOx release, fuel is directly supplied into the exhaust passage 16.

  The catalyst-equipped filter device 18c is composed of a DPF with a catalyst provided with a diesel particulate filter (DPF) for collecting particulate matter (PM) in the exhaust gas. The catalyst-attached DPF is formed of a monolith honeycomb wall flow type filter or the like in which the inlet and outlet of a porous ceramic honeycomb channel are alternately plugged. A catalyst such as platinum or cerium oxide is supported on the filter.

  By this DPF with catalyst, PM in the exhaust gas is collected by the porous ceramic wall. When the amount of collected PM increases, fuel is injected into the exhaust passage 16, the fuel is oxidized by an oxidation catalyst to increase the temperature of the exhaust gas, and the DPF with catalyst is heated by the high-temperature exhaust gas. Is raised to the combustion start temperature of PM, the collected PM is forcibly burned and removed, and the PM regeneration process of the DPF with catalyst is performed.

  Further, in order to measure the temperature Tg of the exhaust gas G, a first temperature sensor 22 at the inlet of the exhaust gas purification device 18, a second temperature sensor 23 for measuring the catalyst temperature Tc of the exhaust gas purification device 18, A λ (excess air ratio) sensor 24 for measuring the excess air ratio (λ) or oxygen concentration in the exhaust gas is provided.

  A control device for inputting the measurement values of these sensors 22, 23, 24 and the like and data necessary for operation control of the engine 10 to perform the operation state of the engine 10 and the exhaust gas purification control and regeneration control of the exhaust gas purification system 1 ( (Not shown) is provided. This control device is provided in a form included in an engine control device called an ECU (engine control unit). This engine control device controls the intake valve 15, the exhaust pipe direct fuel supply device 17, the EGR valve 22, and the like based on the data from the engine 10 and the detected value of the intake air amount sensor 12 and the like.

  In the present invention, the air A1 before pressure increase in the intake passage 11 upstream of the compressor 13a of the turbocharger 13 shown in FIG. 1 is used as the exhaust port for each cylinder (cylinder) 26 that houses the piston 25 as shown in FIG. A first air supply pipe 31 for supplying secondary air to be supplied to 27 is provided. That is, one end side of the first air supply pipe 31 is connected to the downstream side of the air filter of the air cleaner 11a of the intake passage 11 and the upstream side of the compressor 13b, and the other end side is connected to the cylinder head portion of each cylinder 26. It is formed by the provided introduction pipe and connected to the exhaust port 27. Thus, the air A1 before being pressurized by the compressor 13a and after passing through the air filter can be supplied to the vicinity of the exhaust valve 28 upstream of the turbine 13b of the turbocharger 13.

  A reed valve 32 that is a check valve is provided in the first air supply pipe 31, and a first air control valve 33 is provided upstream of the reed valve 32. Further, the diameter of the introduction pipe of the first air supply pipe 31a on the downstream side of the reed valve 32 is relatively set so that the reed valve 32 opens and closes in response to the negative pressure associated with the exhaust pulse rate. Form small.

  As shown in FIG. 3, the reed valve 32 is opened only when the exhaust pressure of the exhaust port 27 is lower than the pressure of the air A1, and the air A1 flows from the first air supply pipe 31 to the exhaust port 27 side. Is acceptable. Further, as shown in FIG. 4, the reed valve 32 is closed when the exhaust pressure of the exhaust port 27 is higher than the pressure of the air A1, and the exhaust gas flows into the first air supply pipe 31a from the exhaust port 27 side. To stop doing.

  By providing the reed valve 32 in the first air supply pipe 31a, the air A1 can be supplied to the exhaust passage 11 efficiently using the pulsation of the exhaust pressure. Further, by providing the first air control valve 33 in the first air supply pipe 31, the flow rate of the air A1 sucked into the exhaust passage 11 side can be controlled.

  Instead of the configuration of the first air supply pipe 32, a passage opened to the atmosphere may be provided to suck in air in the atmosphere. In this case, an air filter for purifying the intake air is provided to prevent foreign matter from entering and reduce the seating noise when the reed valve 32 is closed.

  In the present invention, a second air supply pipe 34 for supplying secondary air is further provided in order to supply the air A2 having been pressurized in the intake passage 11 downstream of the compressor 13a to the exhaust port 27. The second air supply pipe 34 is connected between the reed valve 32 of the first air supply pipe 31 and the first air control valve 33 in FIGS. 2 to 5. You may connect between the reed valve 32 of the supply piping 31, and the exhaust port 27. FIG. The second air supply pipe 32 is provided with a second air control valve 35. The second air control valve 35 turns on and off the passage of the air A2 supplied to the exhaust port 27. Further, the air A2 flowing through the second air supply pipe 34 is cooled by the intercooler 14 by using the intake passage 11 on the downstream side of the intercooler 14 as a connection portion on the upstream side of the second air supply pipe 34. Let it be air.

  The air A2 after the pressure increase is supplied to the exhaust port 27 when the engine speed Ne is relatively large, and the exhaust pressure of the exhaust port 27 is lower than the pressure of the air A2, so as shown in FIG. In addition, the reed valve 32 is always open to allow the air A2 to flow from the first air supply pipe 31 to the exhaust port 27 side.

  An exhaust gas purification method in the exhaust gas purification system 1 will be described. In this exhaust gas purification method, the first air control valve 33 and the second air control valve 35 are controlled, but the reed valve 32 is automatically controlled by the magnitude relationship between the pressure of the air A1, A2 and the pressure of the exhaust port 27. Open and close the valve.

  When the engine is started, it is necessary to activate the NOx occlusion reduction type catalyst 18b of the exhaust gas purification device 18. Therefore, the fuel is supplied to the exhaust gas purification device 18, and the fuel is oxidized in the exhaust gas or the oxidation catalyst 18a of the exhaust gas purification device 18 to raise the temperature of the exhaust gas G, thereby the NOx occlusion reduction type catalyst 18b. The temperature is raised and activated.

  When the engine is started, the temperature of the exhaust passage 16 and the exhaust gas purifying device 18 is not raised. Therefore, when fuel is supplied to the exhaust passage 16, the fuel is supplied by post-injection by cylinder fuel injection control. . This fuel is supplied by an engine control device that controls the injection amount and timing into the combustion chamber.

At the same time, the first air control valve 33 is opened, the second air flow rate control amount valve 35 is closed, and the first air control valve 33 controls the flow rate of the air A1, while the intake air upstream of the compressor 13a is controlled. Air A 1 at atmospheric pressure is supplied from the passage 11 to the exhaust port 27. As a result, the pulsation of the exhaust pressure is utilized, and when the negative pressure is generated, the reed valve 32 provided in the first air supply quick pipe 31 is passed through to suck in the atmospheric air A1, and the exhaust gas purification device 18 Is supplied as secondary air.
The flow rate of the air A1 is controlled by the first air control valve 33 according to the catalyst temperature Tc, the engine speed Ne, and the load Q. In a situation where the engine 10 is started again after the vehicle has traveled, the catalyst temperature Tc may be in the activation temperature range even when the engine 10 is stopped. In such a case, the catalyst is excessive. In such a case, control is performed to reduce the valve opening degree of the first air control valve 33 so as to suppress the supply of the air A1.

  The secondary air supply control at the time of starting the engine is performed, for example, according to a control flow as shown in FIG. That is, when the engine is started and the control flow for supplying secondary air at the time of starting the engine in FIG. 6 is started, the engine speed Ne is set in advance from the rotational speed Ni (engine speed at idling) Ni set in step S11. If it is not large (NO), after a predetermined time (time related to the determination interval of the engine speed Ne) Δt1, the process returns to step S11 and the engine speed Ne is large. Wait until

  If it is determined in step S11 that the engine speed Ne is larger than the preset rotational speed Ni, the process goes to step S12 to determine whether or not the catalyst temperature Tc is smaller than the preset first temperature threshold value T1. The first temperature threshold T1 is set to the activation temperature of the catalyst (for example, about 200 ° C.). If the catalyst temperature Tc is smaller than the first temperature threshold value T1 (YES) in step S12, the process proceeds to the first control in step 13.

  In the first control of step S13, fuel is supplied into the exhaust passage 16 by post injection for injecting fuel into the combustion chamber during the expansion stroke and the exhaust stroke, the first air control valve 33 is opened, and the first control is performed. 2 The air control valve 33 is closed. At the same time, the valve opening degree of the first air control valve 33 is controlled to adjust the air flow rate. The valve opening degree of the first air control valve 33 is calculated with reference to the valve opening degree map based on the detected catalyst temperature Tc. This valve opening degree map is set in advance corresponding to the catalyst temperature Tc such that the lower the catalyst temperature Tc, the larger the first air control valve 33 is opened. The first control is performed for a predetermined time (time related to the catalyst temperature determination interval) Δt2, and then the process returns to step S12.

  If the catalyst temperature Tc is not smaller than the first temperature threshold value T1 in the determination of step S12 (NO), the catalyst is activated and the exhaust gas purifying device 18 is warmed up at the start of the engine, and the process returns. Return to normal operation.

  When starting the engine, the first air supply pipe 31 is connected to the exhaust port 27 in the vicinity of the exhaust valve 28 upstream of the turbine 13b of the turbocharger 13, so that the exhaust valve 28 is closed. The air A1 can be supplied to the exhaust passage 11 using the negative pressure of That is, when the engine 10 is operating, a series of four-cycle strokes are repeated in each cylinder 26, but the exhaust valve 28 is opened in the latter half of the expansion stroke to discharge high-temperature and high-pressure exhaust gas. Thereafter, when the exhaust valve 28 is closed, a negative pressure portion is generated in the exhaust gas due to the inertia of the exhaust gas. Due to this negative pressure, the reed valve 32 disposed in the first air supply pipe 31 is opened as shown in FIG. 3, and atmospheric air A <b> 1 flows into the exhaust port 27. In other cases, since the exhaust pressure is higher, it is not sucked, and the reed valve 32 is closed as shown in FIG.

  By supplying the low-pressure air (or air in the atmosphere) A1 upstream of the compressor 13a upstream of the compressor 13a intermittently according to the exhaust pulsation through the reed valve 32, the exhaust gas is supplied to the air. In a state where the high oxygen concentration portion where A1 is sucked and the high fuel concentration portion where air A1 is not sucked are separated in time, the oxygen is introduced into the catalyst of the exhaust gas purification device 18 and oxygen in the exhaust gas is discharged. After adsorbing on the catalyst as highly reactive oxygen atoms, fuel is supplied to promote the combustion reaction.

  That is, using the fact that the pulsation effect of the exhaust pressure is large when the engine speed Ne is low, the secondary air is intermittently supplied when the catalyst is lower than the activation temperature (purification activation temperature range) T1 immediately after starting the engine. To promote the oxidation of fuel in the oxidation catalyst.

  Further, at the time of desulfurization processing (sulfur purge) for removing the sulfur component accumulated in the exhaust gas purification device 18 or at the time of PM regeneration processing for removing the particulate matter (PM) accumulated in the exhaust gas purification device 18 by combustion. When the temperature is raised and heated, the fuel is supplied to the exhaust gas purification device 18 while properly using the post injection in the cylinder fuel injection control and the direct fuel supply device 17 in the exhaust pipe depending on the exhaust gas temperature Tg.

  At the same time, the first air control valve 32 is closed, the second air control valve 35 is opened, and the flow rate of the air A2 boosted from the intake passage 11 downstream of the compressor 13a is increased by the second air control valve 35. The exhaust port 27 is supplied while being controlled.

  In the temperature rise and heating control when a catalyst temperature higher than the normal catalyst temperature such as desulfurization treatment or PM regeneration treatment is required, a large amount of fuel is supplied to the exhaust gas purification device 18 so as to shorten the temperature rise time. However, it is necessary to supply secondary air at a sufficient flow rate corresponding to a large amount of fuel so as not to run out of oxygen.

  In this state, since the engine speed Ne is not as low as that at the time of idling immediately after the engine is started, the air flow rate is insufficient only by sucking and supplying the secondary air only by the negative pressure due to the exhaust pulsation. Therefore, the pressurized air A2 is supplied to the exhaust port 27 from the downstream side of the compressor 13a of the turbocharger 13 via the second air supply pipe 34 and the second air control valve 35. In this case, the reed valve 36 is normally open because the pressure on the air A2 side is increased. When the catalyst temperature Tc reaches the desulfurizable temperature or the PM combustion start temperature, the second air control valve 35 is also closed and the supply of the secondary air A2 is stopped.

  This control is performed, for example, according to a control flow as shown in FIG. That is, when the engine is started and the control flow for secondary air supply at the time of heating and heating for the desulfurization process and PM regeneration process of FIG. 7 is started, the process mode is the desulfurization process mode in step S21. Whether or not the PM regeneration processing mode is in effect is determined. If it is determined in step S21 that the process mode is neither the desulfurization process mode nor the PM regeneration process mode, the process returns, and the process is terminated without performing the control for supplying the secondary air during the temperature increase and heating. .

  If it is determined in step S21 that the processing mode is one or both of the desulfurization processing mode and the PM regeneration processing mode, the process goes to step S22 to perform the second control. In this second control, the first air control valve 33 is closed and the second air control valve 35 is opened. The second air control valve 35 is fully opened without controlling the air flow rate.

  After the second control, the process goes to step S23 to determine whether or not the exhaust gas temperature Tg is greater than a preset second temperature threshold T2. The second temperature threshold value T2 is a temperature at which the fuel injected by the fuel injection in the exhaust pipe is sufficiently gasified and can be oxidized by the oxidation catalyst 18a. If the exhaust gas temperature Tg is not larger than the second temperature threshold value T2 in the determination of step S23 (NO), the process goes to step S24 to perform post-injection and supply fuel to the exhaust gas device 18 for a predetermined time (exhaust gas temperature). (Time related to determination interval) is supplied for Δt3, and then the process returns to step S23.

  If the exhaust gas temperature Tg is higher than the second temperature threshold value T2 (YES) in step S23, the process goes to step 25. In this step S25, it is determined whether or not the catalyst temperature Tc is smaller than a preset third temperature threshold T3. The third temperature threshold T3 is a desulfurization start temperature (for example, about 700 ° C.) at which the sulfur component of the catalyst begins to be separated in the desulfurization processing mode, and is captured by the filter with catalyst 18c in the PM regeneration processing mode. The collected PM is set to a temperature at which combustion starts (for example, about 550 ° C.).

  If it is determined in step S25 that the catalyst temperature Tc is lower than the third temperature threshold value T3 (YES), the fuel is supplied to the exhaust gas purifying device 18 by direct fuel injection in the exhaust pipe to raise the temperature and heat the catalyst. Supply is performed for time (time related to the catalyst temperature determination interval) Δt4, and then the process returns to step S25.

  In this exhaust pipe direct injection, the operation state during control start or during control changes depending on traffic conditions and cannot be specified. Therefore, the catalyst temperature detected in the temperature raising process with the second air control valve 35 fully opened. Feedback control of the fuel injection amount with respect to Tc is performed. The adjustment of the fuel injection amount is performed by controlling the injection interval of the exhaust pipe direct fuel supply device 17, but a map in which a lower limit value of the injection interval corresponding to the engine speed Ne and the fuel flow rate (related to the load Q) is set in advance. Data is provided, and feedback control of the injection interval based on the catalyst temperature Tc is performed so as not to be below the lower limit value calculated from this map data.

  If it is determined in step S25 that the catalyst temperature Tc is not lower than the third temperature threshold value T3 (NO), it is determined that the catalyst has been sufficiently heated and heated and the process returns. After returning, desulfurization processing or PM regeneration processing is performed according to another control flow (not shown).

  During the desulfurization process or the PM regeneration process, when the catalyst temperature Tc is equal to or higher than the PM combustion temperature or the desulfurizable temperature, the second air control valve 35 is also closed and the supply of the secondary air A2 is stopped. When Tc is likely to decrease, the temperature of the exhaust gas purification device 18 is supplied by supplying the fuel and the secondary air A2 to the exhaust gas purification device 18 by the second control and direct fuel injection in the exhaust pipe as necessary. Is maintained at a temperature suitable for desulfurization treatment or PM regeneration treatment.

  At the time of this temperature rise and heating control, a large amount of air A2 having a high pressure downstream from the compressor 13a is supplied to the exhaust gas via the reed valve 32 and also via the second air control valve 35. The secondary air amount commensurate with the amount of fuel supplied to can be supplied. As a result, the stop of the oxidation reaction due to lack of oxygen can be avoided, and the time required for temperature increase and heating can be shortened by a large amount of heat generation.

  In addition, by introducing air A2 into the exhaust port 27 with the boost pressure required for the torque generated by the engine 10, it is necessary for desulfurization processing and PM regeneration processing even when traveling at low atmospheric pressure such as traveling at high altitudes. A sufficient amount of air (oxygen amount) can be ensured, and the temperature rise and heating control of the catalyst can be performed.

  According to the exhaust gas purification system 1 and the exhaust gas purification method having the above-described configuration, the first air control valve 33 is opened when the temperature of the catalyst at the time of engine start is relatively low, and the first air control valve 33 is opened. By closing the valve 35, the atmospheric pressure air A <b> 1 passes through the first air supply pipe 31 to prevent backflow by the reed valve 32 and adjust the flow rate by the first air control valve 33, while adjusting the flow rate of the exhaust pressure. The exhaust port 27 can be intermittently supplied using the pulsation.

  As a result, the exhaust air pulsation when the engine speed Ne is low is efficiently used to supply the air A1 intermittently as secondary air to the exhaust gas purification device 18, and when the oxygen concentration is high and the fuel concentration is high The exhaust gas can flow into the exhaust gas purification device. Therefore, fuel can be supplied after oxygen is adsorbed on the catalyst as oxygen atoms having high reaction activity, so that the combustion reaction on the catalyst can be significantly accelerated and the temperature of the catalyst can be raised efficiently. it can.

  Further, when the catalyst temperature rises during the desulfurization process where the engine speed Ne is relatively high or the DPF 18c with the catalyst rises during the PM regeneration process, the first air control valve 33 is closed and the second air flow valve 35 is opened. By performing the valve operation, the air A <b> 2 that has been pressurized by the compressor 13 a of the turbocharger 13 can be supplied to the exhaust port 27 via the second air supply pipe 34 and the first air supply pipe 31. At this time, since the pressurized air A2 is higher than the exhaust pressure of the exhaust port 27, the reed valve 32 is always in the open state shown in FIG.

  Thus, the intake air pressure (boost pressure) when the engine speed Ne is high is efficiently used, and air A2 is continuously supplied as a secondary air to the exhaust gas purification device 18 in a sufficient amount, thereby efficiently catalyzing the catalyst. Alternatively, the temperature of the DPF 18c with catalyst can be increased.

  An exhaust gas purification system and an exhaust gas purification method of the present invention include an exhaust gas purification device for an exhaust passage of an internal combustion engine, and, if necessary, fuel is supplied to the exhaust gas purification device by post injection or direct combustion injection in an exhaust pipe. In the exhaust gas purification system to be supplied, when supplying secondary air after the engine is started, atmospheric pressure air is intermittently sucked using exhaust pulsation and exhaust gas with high oxygen concentration and exhaust gas with high fuel concentration Can be supplied to the catalyst alternately in time, and the temperature can be efficiently raised. In addition, in the supply of secondary air during the desulfurization process and the PM regeneration process, the amount of fuel supplied in a large amount in the exhaust passage On the other hand, the temperature of the catalyst can be quickly raised by introducing air pressurized by the compressor and supplying a sufficient amount of air.

  Therefore, the exhaust gas purification system and the exhaust gas purification method of the present invention can be used as an exhaust gas purification system and an exhaust gas purification method in an exhaust passage of an internal combustion engine or the like mounted on an automobile.

1 Exhaust gas purification system 10 Engine (internal combustion engine)
11 Intake passage 13 Turbocharger (supercharger)
13a Compressor 16 Exhaust passage 17 Direct fuel supply device in exhaust pipe 18 Exhaust gas purification device 18a Oxidation catalyst device (DOC)
18b NOx occlusion reduction type catalyst device (LNT)
18c Filter device with catalyst (CSF)
22 First temperature sensor 23 Second temperature sensor 25 Piston 27 Exhaust port 31 First air supply pipe 32 Reed valve (check valve)
33 1st air control valve 34 2nd air supply piping 35 2nd air control valve A1 Air before pressurization (air of atmospheric pressure)
A2 Air after pressure increase G Exhaust gas Ne Engine speed Ni Preset speed Tc Catalyst temperature Tg Exhaust gas temperature T1 Preset first temperature threshold T2 Preset second temperature threshold T3 Preset third temperature threshold

Claims (2)

In an exhaust gas purification system that includes an exhaust gas purification device for an exhaust passage of an internal combustion engine and supplies fuel to the exhaust gas purification device by post injection or direct combustion injection in an exhaust pipe as necessary,
A first air supply pipe for supplying secondary air for supplying air in an intake passage upstream of the compressor of the supercharger or air in a passage communicating with the atmosphere to an exhaust port; and the intake passage downstream of the compressor A secondary air supply pipe for supplying secondary air to the exhaust port, a first air control valve in the first air supply pipe, and a second air control in the second air supply pipe Each provided with a valve, and further provided with a check valve that allows the flow of air to the exhaust port side but prevents the flow of exhaust gas from the exhaust port,
Furthermore, a control device for controlling fuel supply to the exhaust gas purification device and opening / closing of the first air control valve and the second air control valve,
When the engine is started, fuel is supplied to the exhaust gas purification device by post injection, the first air flow control valve is opened, the second air control valve is closed, and the air amount is controlled by the first air control valve. While supplying air to the exhaust port,
At the time of desulfurization processing for removing sulfur components accumulated in the catalyst of the exhaust gas purification device, or at the time of PM regeneration processing for removing particulate matter accumulated in the exhaust gas purification device by combustion, post injection or direct injection in the exhaust pipe The fuel gas is supplied to the exhaust gas purifying device, and the first air control valve is closed and the second air control valve is opened to control to supply air to the exhaust port. Exhaust gas purification system. An exhaust gas purification device for an exhaust passage of the internal combustion engine is provided, and if necessary, fuel is supplied to the exhaust gas purification device by post injection or direct combustion injection in the exhaust pipe,
Furthermore, a first air supply pipe for supplying secondary air that supplies air in an intake passage upstream of a compressor of a supercharger or air in a passage communicating with the atmosphere to an exhaust port, and the downstream side of the compressor A second air supply pipe for supplying secondary air for supplying air from the intake passage to the exhaust port; a first air control valve for the first air supply pipe; and a second air supply pipe for the second air supply pipe. Exhaust gas of an exhaust gas purification system that is provided with an air control valve and further provided with a check valve that permits the flow of air to the exhaust port side but prevents the flow of exhaust gas from the exhaust port In the gas purification method,
When the engine is started, fuel is supplied to the exhaust gas purification device by post injection, the first air flow control valve is opened, the second air control valve is closed, and the air amount is controlled by the first air control valve. While supplying air to the exhaust port,
At the time of desulfurization processing for removing sulfur components accumulated in the catalyst of the exhaust gas purification device, or at the time of PM regeneration processing for removing particulate matter accumulated in the exhaust gas purification device by combustion, post injection or direct injection in the exhaust pipe To supply the fuel to the exhaust gas purification device, close the first air control valve and open the second air control valve, and supply air to the exhaust port.

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