JP2005315189A - Exhaust gas aftertreatment device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce noise at a time of returning an exhaust gas throttle valve 9 to the full open position after closing the exhaust gas throttle valve 9 and oxidizing and removing particulate matter accumulated on a diesel particulate filter 81 and regenerating the filter in a diesel engine provided with EGR valve 7 and the exhaust gas throttle valve 9. <P>SOLUTION: The diesel particulate filter 81 is installed in an exhaust system of the diesel engine provided with EGR valve 7, and a catalyst is installed in an upstream of the filter 81 and the exhaust gas throttle valve 9 is installed in a downstream of the filter 81. The diesel engine is operated under a condition where opening of the exhaust gas throttle valve is small, the exhaust gas throttle valve 9 is returned to the full open position after the EGR valve 7 is opened when the operation is completed if the diesel particulate filter 81 is regenerated. Pressure in the exhaust system is reduced by opening of the EGR valve 7 and noise generated due to opening of the exhaust throttle valve 9 can be greatly reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas aftertreatment device provided in an exhaust system of an engine and a control device thereof in order to reduce harmful components contained in the exhaust gas of a diesel engine, particularly particulate matter regulated by the diesel engine. It is about.

As an important part of environmental measures, regulations for nitrogen oxides (NOx) or hydrocarbons (HC), which are considered harmful components in exhaust gas, are implemented for vehicle engines, while reducing harmful components Various technologies are being developed vigorously. In particular, regulations on diesel engines, particularly diesel engine exhaust gas, have been gradually strengthened in recent years, and there is a tendency that more stringent regulations will be implemented in the future. A diesel engine is an engine that compresses air supplied into a cylinder and injects fuel into air that has become high temperature and pressure and burns it, and generally has higher thermal efficiency than a gasoline engine. Therefore, although the emission amount of carbon dioxide (CO ₂ ) has a characteristic of being reduced by that amount, reduction of particulate matter (particulate: PM) and NOx is strongly demanded.

  In PM, carbon and unburned components of fuel are discharged as fine particles due to incomplete combustion of fuel injected into a cylinder. In a diesel engine, the amount of PM generated increases depending on the operating state due to poor mixing of injected fuel and air. In particular, for the purpose of reducing NOx, when performing so-called EGR, which is mixed with air in a diesel engine cylinder and recirculates exhaust gas, the amount of air supplied into the cylinder is reduced or the maximum combustion temperature Since the amount of generated PM tends to increase due to the decrease in PM, there is a trade-off between reducing PM and controlling NOx by controlling the combustion method.

  EGR for NOx reduction is widely implemented in vehicle engines regardless of whether it is a gasoline engine or a diesel engine. An EGR passage that connects the exhaust passage and the intake passage of the engine is provided, and the exhaust gas is sent to the intake passage of the engine. To reflux. In the EGR passage, an EGR valve that controls the amount of exhaust gas (EGR gas) that recirculates is installed, and the valve opening degree is adjusted according to the operating state of the engine. In general, the EGR gas amount is increased in the middle load region of the engine where the amount of NOx generated is large, and the recirculation is stopped in the low load region and the high load region.

In order to prevent the emission of PM, there is a technique of attaching a filter called a diesel particulate filter (DPF) to the exhaust system of a diesel engine and capturing the PM by this DPF. The DPF is usually a ceramic body such as porous cordierite that is provided with a large number of thin passages partitioned in a lattice pattern in the axial direction, and the entrances and exits of adjacent passages are alternately sealed. The exhaust gas of the diesel engine flows downstream through the porous ceramic wall between adjacent passages, and at this time, particulate PM is collected. Some use a fine non-woven fabric made of heat-resistant fibers such as ceramic fibers instead of using a porous ceramic body. In addition, in order to prevent the emission of PM, a technique for mounting an oxidation catalyst device in which a catalyst made of a noble metal such as platinum, palladium or rhodium is coated on the surface of a large number of passages formed in a ceramic carrier is also known. Yes. When the exhaust gas flows through the passage of the oxidation catalyst device, the catalytic action causes PM in the exhaust gas to react with oxygen in the exhaust gas of the diesel engine and be oxidized to be converted to CO ₂ or the like. In some cases, such a catalyst is supported on the surface of the DPF.

  By the way, in the DPF equipped in a vehicle equipped with a diesel engine, PM captured by the repeated operation of the engine accumulates. When a large amount of PM accumulates, the filter becomes clogged and the back pressure of the engine increases, or the accumulated PM burns at a time when the engine exhaust temperature becomes high and heats up to the DPF. There are harmful effects such as damage. In order to prevent such an adverse effect, it is necessary to regenerate the DPF, in which the accumulated PM is removed as appropriate to restore the DPF function.

  As a regeneration means, a system in which PM is burned by heating with an electric heater or a burner is known. However, when this PM combustion method is adopted, the DPF becomes complicated and expensive due to the combination of an electric heater and the like with the DPF, and at the same time, PM cannot be collected during re-combustion. There arises a problem that the apparatus becomes large in size because a system in which a plurality of DPFs are arranged in parallel in the passage to alternately collect and burn. Based on this problem, in recent years, an oxidation catalyst is installed upstream of the DPF exhaust gas to oxidize unburned components in the exhaust gas and raise its temperature. A method of regenerating DPF by continuously oxidizing and removing during operation is drawing attention. In addition, a method of coating the surface of the DPF instead of installing the catalyst upstream, for example, using a so-called NOx storage reduction catalyst on the upstream surface of the DPF, and utilizing active oxygen generated when NOx is stored and reduced A method of continuously oxidizing and removing the collected PM is also conceivable. A DPF having a catalyst upstream of the DPF and continuously removing and regenerating the collected PM is referred to herein as a continuously regenerating DPF.

  Since the continuous regeneration type DPF removes PM by the action of the catalyst provided upstream thereof, the catalyst does not perform sufficiently below the activation temperature of the catalyst, as in a normal catalyst device, and continuously. Playback is not performed. An activation temperature corresponding to the catalyst characteristics, for example, a temperature of about 350 ° C., is necessary for the catalyst to be activated and to perform good regeneration. However, the exhaust gas temperature is low when the diesel engine has a low fuel injection amount and a low load. If the operating state continues considerably for a long time, the temperature of the catalyst falls below the activation temperature. For this reason, PM is accumulated in the DPF, which causes the DPF to be damaged due to combustion of a large amount of PM when the back pressure of the engine increases or the exhaust gas temperature rises. Therefore, even in a continuous regeneration type DPF, when a certain amount of PM accumulates in the DPF, the PM must be removed by a method such as raising the exhaust gas temperature and activating the catalyst. Regeneration is hereinafter referred to as forced regeneration.

  In order to raise the temperature of exhaust gas from a diesel engine, there is a means called post injection. This means that during the expansion stroke to the exhaust stroke of a diesel engine, the added fuel is injected into the engine cylinder, and the fuel does not burn in the cylinder, but is oxidized and burned mainly in the exhaust pipe and the catalyst placed there. This increases the temperature of the exhaust gas. Generally, a good effect can be obtained by injecting after the end of the expansion stroke. The post-injection has an advantage that no additional device is required because the added fuel is supplied from the fuel injection nozzle originally provided in the cylinder of the diesel engine. The amount and number of post injections can be controlled to adjust the temperature of the exhaust gas to be heated.

  In addition, if the injection timing of the normal fuel injection of a diesel engine, that is, the fuel injection that is injected in the expansion stroke from the end of the compression stroke and burned in the cylinder of the engine, is delayed, the combustion of the fuel that does not contribute to the engine output torque is caused. As a result, the temperature of the exhaust gas increases. In order to realize such a delay in injection timing, so-called multi-injection is preferable. Multi-injection is performed by dividing fuel injection into multiple parts. In a diesel engine, normally, the fuel that is continuously injected from the end of the compression stroke to the expansion stroke is transferred to an injection method in which the fuel is injected in multiple times. It is possible to easily perform controlled delayed injection.

  Although post injection or multi-injection is an effective means for raising the exhaust gas temperature so as to ensure the activity of the catalyst of the continuous regeneration type DPF, there are cases where sufficient temperature rise cannot be obtained by this alone. Therefore, when an exhaust throttle valve is provided downstream of the continuous regeneration DPF and forced regeneration by post injection or the like is performed, the opening of the exhaust throttle valve is reduced to narrow the exhaust passage, and the heat from the continuous regeneration DPF is reduced. A means for promoting the regeneration of the DPF by activating the catalyst by preventing the diffusion of the catalyst and keeping it warm can be considered.

  An exhaust aftertreatment device for a diesel engine that combines a continuously regenerating DPF and an exhaust throttle valve in this manner is known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-343287. When the exhaust is throttled by the exhaust throttle valve, the engine back pressure increases and the load acting on the engine increases, so that the fuel injection amount increases and the exhaust gas temperature further increases. A diesel engine that includes an exhaust aftertreatment device that combines a continuous regeneration type DPF and an exhaust throttle valve and that performs EGR for NOx reduction will be described below with reference to FIG.

  FIG. 4 schematically shows a diesel engine that has a continuously regenerating DPF and an exhaust throttle valve in an exhaust system and recirculates exhaust gas to an intake pipe. Air is supplied into the cylinder of the diesel engine body 1 through an air cleaner 2 and an intake pipe 3. In the cylinder, fuel is injected from the fuel injection nozzle 4 at the end of the compression stroke, and the injected fuel is mixed with the compressed air and burned in the cylinder to generate power. The exhaust gas after combustion is discharged to the exhaust pipe 5 and a part thereof is recirculated to the intake pipe 3 via the EGR passage 6. The recirculation is performed mainly for the purpose of preventing the generation of NOx, and the amount of exhaust gas recirculated is controlled by the EGR valve 7.

  A continuous regenerative DPF 8 is installed in the exhaust pipe 5, and an exhaust throttle valve 9 is installed downstream thereof. The exhaust throttle valve 9 controls a negative pressure from a negative pressure source 93 introduced into a fluid pressure actuator 92 that opens and closes the exhaust throttle valve 9 by an electromagnetic valve 91, and is kept fully open during normal operation of the diesel engine. The continuous regeneration type DPF 8 includes a DPF 81 in which a large number of passages are formed in the axial direction of the ceramic body, and an oxidation catalyst 82 disposed upstream thereof. Further, the continuous regeneration type DPF 8 includes a differential pressure sensor 83 that detects a differential pressure between an upstream pressure and a downstream pressure of the DPF 81, an inlet temperature sensor 84 that detects an exhaust gas temperature upstream of the oxidation catalyst 81, and an outlet side. An outlet temperature sensor 85 that detects the temperature of the DPF 81 (inlet side of the DPF 81) is installed, and detection signals from these sensors are input to the engine control device 10 (ECU).

  During operation of the diesel engine, the fuel injected from the fuel injection nozzle 4 burns in the cylinder, and the exhaust gas after combustion is exhausted to the exhaust pipe 5. A part of the exhaust gas is recirculated to the intake pipe 3 through the EGR passage 6, and the amount thereof is controlled by the EGR valve 7 according to the operating condition of the diesel engine. When the remaining exhaust gas passes through the continuous regeneration type DPF 8, the PM in the exhaust gas is captured by the wall surface between the numerous axial passages formed in the DPF 81, and the exhaust gas from which PM is removed downstream of the DPF 81. Is sent out. During the normal operation of the diesel engine, the PM collected and deposited in the DPF 81 is combined with oxygen and the like in the exhaust gas by the exhaust gas heated to a high temperature by the action of the oxidation catalyst 82, and is oxidized and removed.

  However, when the diesel engine is operated at a low load for a long time, the temperature of the exhaust gas is lowered, the activity of the oxidation catalyst 82 is lowered, and the amount of accumulated PM is increased. The differential pressure between the upstream pressure and the downstream pressure increases. When the temperature detected by the inlet temperature sensor 84 and the outlet temperature sensor 85 of the oxidation catalyst 82 decreases and the differential pressure detected by the differential pressure sensor 83 exceeds a predetermined value, the DPF 81 is forcibly regenerated, so that the exhaust gas The ECU 10 outputs a command for performing post injection so as to increase the temperature of the gas.

The temperature increase of the exhaust gas due to the post injection is carried out while the vehicle is running, but in the low load region of the engine where the catalyst is not activated, the ECU 10 controls the solenoid valve to reduce the opening of the exhaust throttle valve 9. A command is issued to 91 to control the exhaust gas flow strongly. As a result, the downstream side of the continuous regeneration type DPF 8 is throttled, the inside of the continuous regeneration type DPF 8 is kept warm, and the load acting on the engine increases, so that the oxidation catalyst 82 is sufficiently activated and the regeneration of the DPF 81 proceeds. If the EGR valve 7 is open at this time, the exhaust gas flows into the intake pipe and the purpose of restricting the exhaust gas is not achieved. Therefore, the EGR valve 7 is fully closed by the ECU 10.
JP 2003-343287 A

  As described above, in order to oxidize and remove the PM collected by the continuous regeneration type DPF, it is effective to use the exhaust gas at a high temperature by post injection and the exhaust throttle valve in combination. However, if an exhaust throttle valve is provided in the exhaust pipe and the opening thereof is reduced during the forced regeneration of the DPF, the exhaust resistance of the diesel engine is greatly increased, which greatly affects the operation. Therefore, when the exhaust throttle valve is used together in forced regeneration, it is desirable to perform the diesel engine as an idle operation when the vehicle is stopped at an intersection or the like. In addition, the driver can intentionally stop the vehicle for forced regeneration and perform forced regeneration using the exhaust throttle valve together.

  When the forced regeneration operation using the exhaust throttle valve is completed, the exhaust throttle valve needs to be fully opened to return the diesel engine to normal operation. When the exhaust throttle valve is closed, the exhaust pressure of the engine is high and the fuel consumption rate has deteriorated. In addition, due to the necessity of quickly rerunning the stopped vehicle, the return to the exhaust throttle valve fully opened is as short as possible. It is desirable to do in. However, it has been found that an exhaust throttle valve installed downstream of the continuous regeneration type DPF generates loud and harsh noise when it is rapidly returned to full open.

  When the exhaust throttle valve is closed and forced regeneration such as post injection is performed, high-pressure exhaust gas stays upstream of the exhaust pipe. The above noise is caused by the shock pressure wave generated at that time when the exhaust throttle valve is opened and the accumulated exhaust gas instantaneously drops to near atmospheric pressure and flows into the exhaust pipe on the outlet side. To do. The exhaust gas aftertreatment device such as the continuous regeneration type DPF has a larger cross-sectional area than the exhaust pipe and stores a large volume of exhaust gas, so that the noise becomes more severe. An object of the present invention is to reduce noise when the exhaust throttle valve is fully opened in a diesel engine that includes an exhaust throttle valve downstream of the exhaust gas aftertreatment device and recirculates the exhaust gas to the intake pipe.

In view of the above problems, the present invention aims to reduce the noise when the exhaust throttle valve is returned to full open after the forced regeneration operation in the exhaust gas aftertreatment device is completed, and the forced regeneration operation is completed. In some cases, the exhaust throttle valve is fully opened after the EGR valve installed in the EGR passage is opened. That is, the present invention
“Equipped with an exhaust gas aftertreatment device having a diesel particulate filter that collects particulate matter in the exhaust gas and a catalyst installed on the upstream side thereof, downstream of the exhaust gas aftertreatment device Is equipped with an exhaust throttle valve,
In a diesel engine having an EGR passage for returning exhaust gas to the intake pipe and an EGR valve installed in the passage, the EGR passage being connected to the upstream side of the exhaust throttle valve,
In order to oxidize and remove the particulate matter deposited on the diesel particulate filter and regenerate it, the diesel engine was operated with the exhaust throttle valve open and the EGR valve closed. In this case, when the operation of regenerating the diesel particulate filter is finished, the opening of the exhaust throttle valve is increased after the EGR valve is opened.
It is a diesel engine characterized by this.

  The regeneration of the diesel particulate filter is executed when the diesel engine is operated with the opening of the exhaust throttle valve being small and the EGR valve (7) is closed. It is desirable that the diesel engine is set to be operated in an idle state when the vehicle is stopped.

  When regenerating the diesel particulate filter, in order to increase the temperature of the exhaust gas and promote an oxidation reaction or the like, the fuel injection nozzle is used in the expansion stroke or exhaust stroke of the diesel engine as described in claim 3. The fuel can be added by post injection for injecting the fuel.

  By the way, the amount of PM generated and the amount accumulated in the DPF vary depending on the driving condition of the vehicle, and it is difficult to determine the necessity of forced regeneration. Therefore, as in claim 6, when PM accumulates a predetermined amount or more on the diesel particulate filter, an alarm device is installed to inform the driver of this intentional forced regeneration. It is preferable.

  Even with a continuously regenerating DPF having a catalyst upstream of the DPF, there is a need for forced regeneration of the DPF due to a decrease in catalyst activity due to a decrease in exhaust gas temperature. In the forced regeneration of the DPF, it is more effective to use the exhaust throttle together. In order to forcibly regenerate the DPF, the present invention operates the diesel engine with the exhaust throttle valve opened small and the EGR valve closed. This is effective for reducing noise when the exhaust throttle valve is fully opened.

  That is, in the present invention, when PM accumulates a predetermined amount or more in the DPF and this is forcibly regenerated with the opening of the exhaust throttle valve being small, at the end of the regeneration, after opening the closed EGR valve, Return the exhaust throttle valve to full open with a large opening. Since the EGR passage is connected to the upstream side of the exhaust throttle valve, when the EGR valve is opened prior to opening the exhaust throttle valve, the high-pressure exhaust gas stored in the continuous regeneration DPF during forced regeneration is The pressure in the continuous regeneration type DPF quickly decreases. At the time when the opening of the exhaust throttle valve is increased, the pressure in the continuous regeneration type DPF is sufficiently reduced, and the noise generated when the exhaust throttle valve is opened is compared with that in which the EGR valve is not opened first. As a result. In addition, this noise reduction means can be implemented without adding any special device. Note that the sound associated with the exhaust gas flowing into the intake pipe due to the opening of the EGR valve is a sound that propagates inside the engine and hardly leaks outside.

  From the above effects, it is obvious that the exhaust throttle valve need not be opened after the EGR valve is fully opened. That is, after the opening of the EGR valve starts, when the pressure in the continuously regenerating DPF decreases to such a level that no noise is generated, the exhaust throttle valve can be opened. The operation of the EGR valve naturally includes such an operation.

  When the regeneration of the continuous regeneration type DPF equipped in the exhaust system of a diesel engine is executed with the exhaust throttle valve opening being made small, the load acting on the engine increases, which greatly affects the operation of the vehicle. Effect. As described in claim 2, when this regeneration is performed by driving the diesel engine in an idle state when the vehicle stops, it is possible to avoid the influence on the vehicle operation.

  In the forced regeneration of the DPF, in order to increase the temperature of the exhaust gas and promote the oxidation reaction, when adding fuel by post-injection in which fuel is injected from the fuel injection nozzle as described in claim 3, originally a diesel engine Since it is supplied from the fuel injection nozzle equipped in the above, no special device for fuel addition is required.

When a warning device is installed to notify the driver when PM is deposited on the diesel particulate filter in a predetermined amount or more as in claim 4, the driver is surely required to perform forced regeneration. Therefore, it is possible to take appropriate measures such as intentionally stopping the vehicle for forced regeneration.

  Hereinafter, an exhaust gas aftertreatment device for a diesel engine according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an exhaust gas aftertreatment device for a diesel engine according to the present invention. Components corresponding to those of the conventional example (FIG. 4) and devices are denoted by the same reference numerals. FIG. 2 is a graph showing a change in internal pressure of the continuous regeneration type DPF when the control according to the present invention is performed.

  The basic equipment constituting the exhaust gas aftertreatment device for a diesel engine of the present invention and the operating method thereof are not particularly different from the conventional device shown in FIG. That is, in the cylinder of the diesel engine body 1, the fuel injected from the fuel injection nozzle 4 is mixed with the air supplied from the intake pipe 3 and burned, and the exhaust gas after combustion is discharged to the exhaust pipe 5. The Part of the exhaust gas is recirculated from the EGR passage 6 to the intake pipe 3 and recirculated into the cylinder. The amount is adjusted by operating the EGR valve 7 provided in the EGR passage 6 with a fluid pressure actuator or the like in accordance with a command from the ECU 10. Incidentally, the diesel engine is equipped with a so-called common rail type fuel injection device that injects fuel into each cylinder of the engine by a fuel injection nozzle controlled by a solenoid valve from a fuel storage pipe (common rail). It is possible to inject while precisely controlling the injection timing.

  A continuous regeneration type DPF 8 having a DPF 81 and an oxidation catalyst 82 upstream thereof is installed in the exhaust pipe 5. The DPF 81 is a so-called wall flow type honeycomb filter in which a large number of passages are formed in parallel in a porous ceramic body made of cordierite and the inlets and outlets of the passages are alternately closed, and the exhaust gas Collects PM contained in when passing through the wall surface between passages.

The oxidation catalyst 82 is a catalyst made of a noble metal such as platinum, palladium, or rhodium on the surface of a carrier made of, for example, honeycomb cordierite by coating activated alumina or the like to form a washcoat layer. Those carrying an active ingredient are used. The oxidation catalyst 82 oxidizes HC and CO, which are unburned components in the exhaust gas, to generate H ₂ O and CO ₂ , or oxidizes NO to generate NO ₂ . In such a reaction process of the oxidation catalyst 82, heat is generated and the temperature of the exhaust gas rises. Therefore, PM trapped in the DPF 81 is oxidized and removed, and the DPF 81 is normally regenerated continuously. Of course, it is possible to use other commonly used devices as the DPF 81 or the oxidation catalyst 82. For example, as the DPF 81, a DPF whose surface is coated with a catalyst similar to the above oxidation catalyst or the like is used. It can also be used.

  An exhaust throttle valve 9 is installed downstream of the continuous regeneration type DPF 8. The exhaust throttle valve 9 is a commonly used butterfly valve, and is operated by a fluid pressure actuator 92 that uses a negative pressure from a negative pressure source 93 as a working fluid. Then, by introducing the atmosphere to the fluid pressure actuator 92 via the electromagnetic valve 91, the exhaust throttle valve 9 is held fully open during normal operation of the diesel engine, thereby preventing an increase in exhaust resistance of the diesel engine. Yes. 4, the continuous regeneration type DPF 8 includes a differential pressure sensor 83 that detects a differential pressure between the upstream pressure and the downstream pressure of the DPF 81, and exhaust gas on the inlet side and the outlet side of the oxidation catalyst 81. An inlet temperature sensor 84 and an outlet temperature sensor 85 for detecting the gas temperatures are provided, and detection signals from these sensors are input to the engine control device 10 (ECU).

  As described above, when the diesel engine 1 is operated at a low load for a long time, the temperature of the exhaust gas is lowered, the activity of the oxidation catalyst 82 is lowered, and the accumulation amount of PM collected in the DPF 81 is increased. Therefore, it is necessary to perform forced regeneration of the DPF 81 by means such as an increase in injected fuel or post injection. Such a forced regeneration is set to be performed automatically when the vehicle is running, and when the engine is idling due to a temporary stop of the vehicle at an intersection or the like, the exhaust throttle valve 9 is turned off. Forced regeneration is set as the aperture position. However, depending on the driving situation of the vehicle, the accumulated amount of DPF may be large, and forced regeneration using the exhaust throttle valve 9 together with intentionally stopping the vehicle may be required. Noise is generated when the exhaust throttle valve 9 whose opening is reduced during forced regeneration is fully opened, whether it is a temporary stop during vehicle operation or an intentional stop. The present invention will be described with reference to an example of a simple stop and the subsequent full open return of the exhaust throttle valve 9.

  In the exhaust gas aftertreatment device of the present invention, a manual regeneration switch 11 that is operated by the driver to perform forced regeneration using the exhaust throttle valve 9 intentionally with the vehicle stopped and the engine idling is provided. A pilot lamp 12 and a warning lamp 13 are installed to inform the driver of the necessity of such forced regeneration.

  When the amount of PM trapped in the DPF 81 increases due to a decrease in the temperature of the exhaust gas, the differential pressure between the upstream pressure and the downstream pressure of the DPF 81 increases. In the present invention, when the temperatures detected by the inlet temperature sensor 84 and the outlet temperature sensor 85 with the oxidation catalyst 82 are equal to or lower than a predetermined value and the differential pressure detected by the differential pressure sensor 83 exceeds the first predetermined value, the pilot The driver is urged to stop the vehicle and press the manual regeneration switch 11 for the forced regeneration using the lamp 12 blinking and the throttle valve 9 together.

  When the driver presses the manual regeneration switch 11 in response to the blinking of the pilot lamp 12, the control device of the exhaust gas aftertreatment device enters a forced regeneration standby state. At this time, when the driver stops the vehicle, returns the accelerator pedal, and the diesel engine 1 is in the idle operation state, the forced regeneration of the DPF 81 using the throttle valve 9 is started. In order to perform this control, the detection signal of the accelerator pedal position sensor 14 and the rotation speed signal from the engine rotation speed sensor 15 input to the ECU 10 are used.

  In this forced regeneration, the solenoid valve 91 is switched to introduce a negative pressure to the fluid pressure actuator 92, thereby reducing the opening of the exhaust throttle valve 9 to strongly throttle the exhaust pipe 5, and bringing the diesel engine 1 into an idle state. Feedback control is performed with the idling speed as a target value so as to be maintained. Further, since the EGR passage 6 is connected upstream of the exhaust throttle valve 9, it is necessary to stop the recirculation of the exhaust gas from the exhaust pipe 5 to the intake pipe 3 in order to throttle the exhaust pipe 5 and increase the engine exhaust pressure. There is. During forced regeneration when the exhaust throttle valve 9 is closed, the EGR valve 7 is held fully closed by the ECU 10.

  In the above feedback control, even if the target value of the rotational speed is the idle rotational speed, the load acting on the diesel engine is increased due to the restriction of the exhaust pipe 5, so that more fuel is consumed than in the normal idle state. As a result, the temperature of the exhaust gas increases. Further, in order to further raise the temperature of the exhaust gas, in this embodiment, both multi-injection and post-injection means are used. That is, by first shifting to the multi-injection, the temperature of the exhaust gas is raised by substantially delaying the injection timing of the fuel injected in the expansion stroke from the end of the compression stroke. After the temperature of the inlet temperature sensor 84 of the oxidation catalyst 82 rises to a certain value or more by multi-injection, post-injection is performed in the expansion stroke or exhaust stroke of the diesel engine. When the temperature of the exhaust gas is raised in advance as described above, a good oxidation reaction in the oxidation catalyst 82 of the fuel added by the post injection is ensured, and the regeneration of the DPF 81 is performed smoothly. It is possible to make more precise adjustments such as dividing the injection amount of the post injection into multiple stages and increasing the injection amount in accordance with the temperature rise of the oxidation catalyst 82.

  Despite the blinking of the pilot lamp 12, if the driver does not operate the manual regeneration switch 11 or forcibly regenerates for some reason, PM will continue to accumulate in the DPF 81 and the differential pressure detected by the differential pressure sensor 83. Increases further. When the differential pressure reaches the second predetermined value as the amount of accumulated PM increases, the flashing cycle of the pilot lamp 12 is shortened so as to flash quickly, thereby prompting the driver to perform early forced regeneration. Accordingly, when the driver does not perform forced regeneration and PM accumulation continues and the differential pressure reaches the third predetermined value, the warning lamp 13 is turned on. The warning lamp 13 gives a warning to the driver because a large amount of PM is accumulated in the DPF 81 in this state, and if forced regeneration is performed, the amount of heat generated by the oxidation combustion of the PM becomes excessive, and the DPF 81 and the like are This is because there is a risk of damage. When the warning lamp 13 is turned on, the driver carries the vehicle into a maintenance shop or the like, and here, the accumulated PM is removed by a method such as so-called backwashing or combustion taking a long time. As described above, the exhaust aftertreatment device of the present invention is provided with a three-stage alarm means according to the amount of accumulated PM, and gives the driver a detailed forced regeneration instruction.

  When forced regeneration is started and oxidation / removal of PM by post injection continues for a certain period of time, regeneration of the DPF 81 is completed. After the regeneration is completed, post-injection is stopped, and atmospheric pressure is further introduced into the fluid pressure actuator 92 via the electromagnetic valve 91 to return the exhaust throttle valve 9 to full open. In the present invention, before increasing the opening degree of the exhaust throttle valve 9, the ECU 10 outputs a command for opening the EGR valve 7 that has been fully closed during the forced regeneration. Since the inlet of the EGR passage 6 is located upstream of the exhaust throttle valve 9, when the EGR valve 7 is opened, the high-pressure exhaust gas stored in the continuous regeneration type DPF 8 at the time of forced regeneration is changed to the EGR passage 6. As shown in FIG. 2, the pressure in the continuous regeneration type DPF 8 quickly decreases.

  As described above, when the opening of the exhaust throttle valve 9 installed downstream of the continuous regeneration type DPF 8 is fully opened, a large noise is generated due to the rapid opening of the high-pressure exhaust gas stored therein. To do. In the present invention, the EGR valve 7 is opened before the exhaust throttle valve 9 is opened. Therefore, when the exhaust throttle valve 9 is opened, the pressure in the continuous regeneration type DPF 8 is sufficiently reduced to near atmospheric pressure, and the generated noise is greatly reduced compared with the case where the EGR valve is not opened in advance. It becomes possible to reduce. Moreover, this noise reduction is possible by operating an EGR valve originally installed in a diesel engine, and can be carried out without requiring any additional device.

  By the way, when the EGR valve 7 is opened, the exhaust gas stored in the continuous regeneration type DPF 8 during the forced regeneration causes a rapid pressure drop, so that some sound is generated. However, the exhaust gas at this time flows back to the intake pipe 3 through the EGR passage 6 and flows into the cylinder of the diesel engine body 1. That is, since the exhaust throttle valve 9 is not discharged to the outside as when the exhaust throttle valve 9 is opened, the generated sound is hardly transmitted to the outside.

  FIG. 3 shows the transition (solid line) of the noise level when the EGR valve 7 is opened prior to the opening of the exhaust throttle valve 9 based on the present invention (solid line) in which the valve is not opened (broken line). It shows in comparison with. From this figure, in the conventional one, the noise level at the time is greatly reduced in the present invention compared to the noise level greatly increasing when the exhaust throttle valve 9 is opened. I understand. When the exhaust throttle valve 9 is opened, the exhaust pressure decreases to almost atmospheric pressure, and the diesel engine returns to the normal idle operation state. Therefore, the noise level is also lower than during forced regeneration with high exhaust pressure. ing.

  The above-mentioned embodiment is a case where the vehicle is intentionally stopped and the engine is operated for forced regeneration. However, the forced regeneration using the exhaust throttle valve 9 at the temporary stop while the vehicle is operating is used. Of course, the present invention is also applied to the full open return when the operation is completed. At the time of re-starting after a temporary stop, since a fully responsive return is required to ensure drivability, the present invention in which the pressure of the exhaust system rapidly decreases due to the opening of the EGR valve 7 is advantageous in this respect as well. Demonstrate the effect.

  As described above in detail, the present invention provides a continuous regeneration type DPF as an exhaust gas aftertreatment device, and has an exhaust throttle valve downstream thereof. Further, in a diesel engine having an EGR device, the exhaust throttle valve is closed and the DPF is closed. In order to reduce the noise when the exhaust throttle valve is fully opened after the forced regeneration to remove the PM accumulated on the exhaust is completed, the EGR valve installed in the EGR passage is opened before the exhaust throttle valve is fully opened. The valve is opened. Therefore, the continuously regenerating DPF is not limited to the catalyst as described in the above-described embodiment and is installed upstream of the DPF. For example, for the continuously regenerating DPF in which the catalyst is coated on the surface of the DPF. The present invention is also applicable. It is also apparent that means other than post-injection or multi-injection can be adopted as means for raising the exhaust gas temperature in forced regeneration, for example, using a fuel addition device attached to the exhaust system.

It is the schematic of the exhaust-gas aftertreatment apparatus of the diesel engine based on this invention. It is a figure which shows the change of the internal pressure of the continuous regeneration type | mold DPF based on control of this invention. It is a graph which shows the fall of the noise by this invention. It is the schematic which shows the exhaust-gas aftertreatment apparatus of the conventional diesel engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine body 4 Injection nozzle 5 Exhaust pipe 6 EGR passage 7 EGR valve 8 Continuous regeneration type DPF
81 DPF
82 Oxidation catalyst 83 Differential pressure sensor 9 Exhaust throttle valve 10 Engine control unit (ECU)
11 Manual regeneration switch 12 Pilot lamp 13 Warning lamp

Claims (4)

An exhaust gas aftertreatment device (8) having a diesel particulate filter (81) for collecting particulate matter in the exhaust gas and a catalyst (82) installed on the upstream side thereof, An exhaust throttle valve (9) is installed downstream of the exhaust gas aftertreatment device (8), and
An EGR passage (6) for recirculating the exhaust gas to the intake pipe (3) and an EGR valve (7) installed in the passage are provided, and the EGR passage (6) is disposed upstream of the exhaust throttle valve (9). In a connected diesel engine,
In order to oxidize and remove the particulate matter deposited on the diesel particulate filter (81) and regenerate it, the opening of the exhaust throttle valve (9) is made small and the EGR valve (7) is closed. When the diesel engine is operated in this state, after the regeneration operation of the diesel particulate filter (81) is completed, the exhaust gas throttle valve (7) is opened after the EGR valve (7) is opened. 9) Diesel engine characterized by having a large opening The operation of the diesel engine in a state where the opening of the exhaust throttle valve (9) for regenerating the diesel particulate filter (81) is made small and the EGR valve (7) is closed is The diesel engine according to claim 1, wherein the diesel engine is set to be operated in an idle state when the vehicle is stopped. The diesel engine according to claim 1 or 2, wherein when regenerating the diesel particulate filter (81), the added fuel is injected from the fuel injection nozzle (4) in an expansion stroke or an exhaust stroke of the diesel engine. . An alarm device (12, 13) is installed to notify the driver when particulate matter in the exhaust gas accumulates on the diesel particulate filter (81) in a predetermined amount or more. Item 4. The diesel engine according to any one of Items 3.

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