JP4701622B2 - Diesel engine exhaust gas aftertreatment device - Google Patents

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, the reduction of PM and the reduction of NOx are contradictory.

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. A temperature of about 350 ° C. is necessary as a temperature at which the catalyst is activated and good regeneration is performed. However, the exhaust gas temperature is considerably lowered at a low load when the fuel injection amount of the diesel engine is small, and this operation state is maintained for a long time. If continued, the temperature of the catalyst will be 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 increasing 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 is because, 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. In general, good results can be obtained by injecting after the end of the exhaust 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. Thus, an exhaust gas aftertreatment device for a diesel engine that combines a continuously regenerating DPF and an exhaust throttle valve is known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-343287. If the exhaust gas is throttled, the engine back pressure rises and the load acting on the engine increases, so that the fuel injection amount increases and the exhaust gas temperature further rises. Hereinafter, with reference to FIG. 5, a description will be given of an exhaust aftertreatment apparatus of the diesel engine.

FIG. 5 schematically shows a diesel engine that has a continuously regenerating DPF and an exhaust throttle valve and drives a vehicle. 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 operation of the exhaust throttle valve 9 is performed by controlling the negative pressure introduced into the fluid pressure actuator 92 by the three-way electromagnetic valve 91. During normal operation of the diesel engine, atmospheric pressure is introduced into the fluid pressure actuator 92 and the exhaust throttle valve 9 is held fully open. 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. When the 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 is sent downstream of the DPF 81. It is. 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. At the same time, the ECU 10 outputs a command for switching the three-way solenoid valve 91 in order to reduce the opening of the exhaust throttle valve 9, and the negative pressure source such as the vacuum pump 93 or a negative pressure tank connected thereto is supplied. The pressure is guided to the fluid pressure actuator 92, the opening of the exhaust throttle valve 9 is made very small, and the flow of exhaust gas is strongly throttled.

  In this forced regeneration, the fuel supplied by the post injection is oxidized and burned in the exhaust pipe 5 or the oxidation catalyst 82, and the exhaust gas temperature becomes high. Further, the downstream side of the continuous regeneration type DPF 8 is throttled by the exhaust throttle valve 9, 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. To do. When the regeneration of the DPF 81 is completed, the exhaust throttle valve 9 is returned to the fully open state again.

By the way, when opening the exhaust throttle valve installed in the exhaust pipe, it is known to open the valve by a slow operation. For example, in Japanese Patent Laid-Open No. 2000-337173, when an exhaust throttle valve provided in an exhaust system is opened from a closed position for promoting warming of a diesel engine, the opening operation is slowed to avoid a sudden change in engine torque Techniques to do this are disclosed.
JP 2003-343287 A JP 2000-337173 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 stop the vehicle and perform the diesel engine as an idle operation.

  Further, when the forced regeneration is finished and the PM collected in the DPF is removed, it is necessary to return the exhaust throttle valve to full open in order to return the diesel engine to normal operation. 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 this time as the exhaust throttle valve opens and the accumulated exhaust gas instantaneously drops to near atmospheric pressure and flows into the downstream exhaust pipe. Is. Further, the post-processing 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 again in a diesel engine in which a continuous regeneration type DPF and an exhaust throttle valve are combined.

In view of the above problems, the present invention efficiently executes forced regeneration in a continuous regeneration type DPF having an exhaust throttle valve on the downstream side , and returns the exhaust throttle valve to full open after the forced regeneration is completed. For the purpose of reducing the noise at the time, when the forced regeneration is finished, a valve opening speed reducing means for gradually increasing the opening of the exhaust throttle valve is provided. That is, the present invention
“A continuously regenerating DPF having a diesel particulate filter that collects particulate matter in exhaust gas and a catalyst installed on the upstream side thereof, and further downstream of the continuous regenerating DPF In a diesel engine with an exhaust throttle valve installed,
The continuous regeneration type DPF is provided with a temperature sensor for detecting an exhaust gas temperature,
When the exhaust gas temperature detected by the temperature sensor is equal to or lower than a predetermined value, the vehicle is stopped, and the diesel engine is operated in an idle state, particulate matter deposited on the diesel particulate filter is Start forced regeneration to remove and oxidize ,
During the forced regeneration, the opening of the exhaust throttle valve is kept small, the opening of the diesel engine is maintained at an idle speed, and fuel injection is performed in the exhaust stroke of the diesel engine. Injecting the added fuel from the nozzle, increasing the injection amount of the added fuel in the exhaust stroke as the exhaust gas temperature detected by the temperature sensor increases,
When the forced regeneration is finished, there is provided a valve opening speed relaxation means for gradually increasing the opening of the exhaust throttle valve. ' '
It is a diesel engine characterized by this.

  According to the present invention, in the present invention, the exhaust throttle valve is opened and closed by a fluid pressure actuator, and an orifice is installed in a passage for introducing fluid pressure into the fluid pressure actuator to provide valve opening speed reduction means. It is preferable.

In order to regenerate the diesel particulate filter, as described in claim 3, when particulate matter in the exhaust gas is accumulated in a predetermined amount or more on the diesel particulate filter, this is notified to the driver. It is preferable that an alarm device for notifying is installed. Further, as described in claim 4, when the manual switch is installed together with the alarm device and the manual switch is turned on, when the vehicle is stopped and the diesel engine is operated in the idle state, The particulate filter can be set to be regenerated.

  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, and the present invention is effective when the diesel engine is operated with the opening of the exhaust throttle valve being small for the forced regeneration of the DPF. This is effective for reducing noise when the throttle valve is fully opened. That is, according to the present invention, when the opening of the exhaust throttle valve is reduced, the vehicle stops, and the diesel engine is operated in an idle state and forced regeneration is performed, the exhaust throttle valve is rapidly turned on at the end of the regeneration. There is provided a valve opening speed relaxation means for gradually increasing the opening degree without opening the valve fully. As a result, the rapid release of the high-pressure exhaust gas stored in the exhaust pipe and the continuous regeneration type DPF is avoided, and the pressure drop in the continuous regeneration type DPF when the exhaust throttle valve is opened is moderated. Therefore, the noise generated when the exhaust throttle valve is opened results in a significant reduction as compared with the conventional one without the valve opening speed reducing means.

  Incidentally, it is disclosed in Patent Document 2 that the valve opening speed is slow when the exhaust throttle valve installed in the exhaust pipe is opened. However, the exhaust throttle valve described therein is located relatively upstream of the exhaust system, and a device with a large volume such as a continuously regenerating DPF is not provided upstream of the exhaust throttle valve. The purpose of slowing down the valve opening speed is to prevent a sudden change in engine torque, and there is no description of noise generated when the exhaust throttle valve is opened.

On the other hand, the exhaust throttle valve to which the present invention is applied is installed downstream of a large-capacity device such as a continuous regeneration type DPF, and is used for an operation for regeneration of the DPF. is there. Noise when opening the exhaust throttle valve is a phenomenon that appears conspicuously when a large amount of high-pressure exhaust gas causes a rapid pressure drop, and is a problem peculiar to the release of exhaust gas stored in a large-volume device. . Further, the regeneration of the DPF of the present invention is performed by operating the diesel engine in an idle state. In idling operation, the noise level is lower than the engine noise during vehicle travel and other noises associated with travel, so the noise when the exhaust throttle valve is opened gives a very harsh and unpleasant impression. As described above, the valve opening speed reducing means when the exhaust throttle valve is opened in the present invention exhibits a unique effect that does not exist in the conventional one.
Also, in the forced regeneration of DPF, in order to increase the temperature of exhaust gas and promote the oxidation reaction, fuel is added by post-injection from the fuel injection nozzle originally installed in the diesel engine, so a special device for fuel addition Is not required.

  Engine exhaust throttle valves and the like are often operated by fluid pressure actuators. Therefore, as described in claim 2, when the exhaust throttle valve is opened and closed by the fluid pressure actuator, an orifice is provided in a passage for introducing the fluid pressure into the fluid pressure actuator to serve as a valve opening speed reducing means. Convenient and costs little. However, for example, means for gradually opening the exhaust throttle valve by reducing the switching speed of the electromagnetic valve that switches the fluid pressure to be introduced into the fluid pressure actuator may be employed.

If a warning device is installed to notify the driver when PM has accumulated a predetermined amount or more in the DPF as in claim 3 , the driver can surely determine the necessity of forced regeneration, and Can be dealt with. Further, when a manual switch is provided as in claim 4 , when the manual switch is inserted, the regeneration can be surely executed when the condition for forced regeneration is satisfied.

  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 view of an exhaust gas aftertreatment device for a diesel engine according to the present invention. Components corresponding to those of the conventional example (FIG. 5) and devices are denoted by the same reference numerals. FIG. 2 schematically shows an exhaust throttle valve and an operating device according to the present invention.

  The basic equipment and operation of the exhaust gas aftertreatment device for a diesel engine of the present invention is 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. Is done. 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. As shown in FIG. 2, the exhaust throttle valve 9 is a commonly used butterfly valve, and is operated by a diaphragm-type fluid pressure actuator 92. To the fluid pressure actuator 92, a negative pressure from a negative pressure source such as a vacuum pump 93 or a clean atmosphere introduced through a filter is switched by a three-way electromagnetic valve 91 and guided. During normal operation of the diesel engine, atmospheric pressure is guided to the fluid pressure actuator 92 by the three-way solenoid valve 91, and the exhaust throttle valve 9 is held fully open to prevent an increase in exhaust resistance of the diesel engine. Similarly to the conventional example of FIG. 5, 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 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).

  In this embodiment, a diaphragm type actuator using a negative pressure as an operating source is used as the fluid pressure actuator 92, but other actuators can naturally be used. For example, many large diesel engines are provided with a compressor for compressing air and an air tank as auxiliary machines. In such engines, it is preferable to employ an actuator using compressed air as an operating source as the fluid pressure actuator 92.

  In the present invention, an orifice 94 that restricts the flow of fluid passing through the passage 95 connecting the three-way solenoid valve 91 and the fluid pressure actuator 92 is disposed. The orifice 94 restricts the flow when the three-way solenoid valve 91 is switched to slow the response of the fluid pressure actuator 92. When the orifice 94 is placed in the passage 95, the exhaust throttle valve 9 is opened and closed. Both actions are slow. In order to reduce only the opening speed of the exhaust throttle valve 9, as shown by a broken line in FIG. 2, the orifice 94 may be installed at the air supply port. In order to reduce only the opening speed, a so-called negative pressure delay valve in which an orifice and a check valve are arranged in parallel is placed in the passage 95, and the orifice acts only when the atmosphere flows toward the fluid pressure actuator 92. There are also means to do so. Further, since the orifice 94 is a fluid throttle, a tube having a very thin diameter can be used instead.

  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 during driving of the vehicle, but depending on the driving conditions of the vehicle, the amount of accumulated DPF becomes large and the exhaust throttle valve 9 is used together. Forced regeneration may be required. In the exhaust gas aftertreatment device of the present invention, a manual regeneration switch 11 operated by the driver to perform forced regeneration using the throttle valve 9 is provided, and the necessity of such forced regeneration is further notified to the driver. A pilot lamp 12 and a warning lamp 13 are installed.

  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 electromagnetic valve 91 is switched to introduce a negative pressure from a negative pressure source such as the vacuum pump 93 to the fluid pressure actuator 92, the opening of the exhaust throttle valve 9 is reduced, and the exhaust pipe 5 is strongly throttled. Then, feedback control is performed with the idling speed as a target value so as to maintain the diesel engine in the idling state. Here, even if the target value of the rotational speed is the idle rotational speed, since the load acting on the diesel engine is increased due to the throttle of the exhaust pipe 5, more fuel is injected 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 above a certain value by multi-injection, post-injection is performed at the end of the expansion stroke of the diesel engine 1 or at the exhaust stroke. 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, the three-way electromagnetic valve 91 is switched to guide the atmospheric pressure to the fluid pressure actuator 92 and the exhaust throttle valve 9 is returned to the fully open state. In the present invention, however, the orifice 94 placed in the passage 95 Due to the action, the speed of the fluid pressure actuator 92 at this time becomes a low speed. Therefore, the exhaust throttle valve 9 gradually increases its opening, and it is avoided that the high-pressure exhaust gas stored in the upstream continuous regeneration type DPF 8 is suddenly dropped. The noise generated will be greatly reduced.

  FIG. 3 shows a pressure change in the continuous regeneration type DPF 8 when the three-way solenoid valve 91 is switched to open the exhaust throttle valve 9. As can be seen from the above, by providing the orifice 94 of the present invention, the time (pressure reduction time) until the pressure drop becomes gentle and the atmospheric pressure state is prolonged as compared with the conventional apparatus without the orifice. Further, the pressure reduction time increases as the diameter of the orifice is reduced. That is, it is clear that the rapid opening of the high-pressure exhaust gas is prevented when the orifice is installed.

  FIG. 4 is a graph showing the relationship between the pressure reduction time and the noise level generated. As shown, by providing the orifice 94 of the present invention, the noise level associated with the opening of the exhaust throttle valve 9 is greatly reduced as compared with the conventional one without the orifice. The noise level decreases as the decompression time increases, that is, as the diameter of the orifice decreases. In the exhaust gas aftertreatment device of this embodiment, when the diameter of the orifice is 1 mm, the noise level (A characteristic) is reduced by 10 dB or more compared to the conventional one.

  As described in detail above, the present invention is a forced exhaust system that removes PM accumulated in the DPF by closing the exhaust throttle valve in a diesel engine equipped with a continuous regeneration type DPF and combined with the exhaust throttle valve as an exhaust gas aftertreatment device. For the purpose of reducing noise when the exhaust throttle valve is fully opened after the regeneration is completed, a valve opening speed reducing means for gradually increasing the opening degree of the exhaust throttle valve is provided. The continuous regeneration type DPF is not limited to the catalyst as described in the above-described embodiment and is installed upstream of the DPF. For example, the continuous regeneration type DPF has a catalyst coated on the surface of the DPF. The invention can be applied. 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 the schematic of the exhaust throttle valve and operating device based on this invention. It is a graph which shows the pressure change in an exhaust pipe by 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

1 Diesel engine body 4 Injection nozzle 5 Exhaust pipe 8 Continuous regeneration type DPF
81 DPF
82 Oxidation catalyst 83 Differential pressure sensor 9 Exhaust throttle valve 91 Three-way solenoid valve 92 Fluid pressure actuator 94 Orifice 10 Engine controller (ECU)
11 Manual regeneration switch 12 Pilot lamp 13 Warning lamp

Claims (4)

A continuous regenerative DPF (8) having a diesel particulate filter (81) for collecting particulate matter in exhaust gas, and a catalyst (82) installed upstream thereof; In the diesel engine in which the exhaust throttle valve (9) is installed downstream of the regenerative DPF (8),
The continuous regeneration type DPF (8) is provided with temperature sensors (84, 85) for detecting the exhaust gas temperature,
When the exhaust gas temperature detected by the temperature sensors (84, 85) is equal to or lower than a predetermined value, the vehicle stops, and the diesel engine is operated in an idle state, the diesel particulate filter (81 ) To start the forced regeneration to remove the particulate matter deposited in
During the forced regeneration, the opening of the exhaust throttle valve (9) is kept small, the opening is maintained, the rotational speed of the diesel engine is maintained at an idle rotational speed, and the exhaust stroke of the diesel engine is increased. Injecting the added fuel from the fuel injection nozzle (4) at the same time, increasing the injection amount of the added fuel in the exhaust stroke as the exhaust gas temperature detected by the temperature sensor (84, 85) increases ,
A diesel engine characterized in that valve opening speed mitigation means for gradually increasing the opening of the exhaust throttle valve (9) is provided at the time when forced regeneration is finished. The exhaust throttle valve (9) is opened and closed by a fluid pressure actuator (92), and the valve opening speed reducing means is an orifice (94) installed in a passage for introducing fluid pressure into the fluid pressure actuator (92). The diesel engine according to claim 1, wherein The alarm device (12, 13) according to claim 1 or 2, wherein when a predetermined amount of particulate matter is deposited on the diesel particulate filter (81), an alarm device (12, 13) is provided to notify the driver. diesel engine. When the manual switch (11) is installed together with the alarm device (12, 13) and the manual switch (11) is turned on, when the vehicle stops and the diesel engine is operated in an idle state, The diesel engine according to claim 3, wherein the diesel particulate filter (81) is set to start forced regeneration .

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