JP2006266221A - Rising temperature controller of aftertreatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the temperature of a catalyst from being excessively raised after the temperature rising control of an aftertreatment device is completed. <P>SOLUTION: The electronic control unit 10 of this rising temperature controller promotes the cooling of the catalyst 42 by performing an exhaust gas flow maintenance control until a catalyst temperature detected by a catalyst outlet exhaust gas temperature sensor 60 reaches a threshold or below after the temperature rising control for regenerating the catalyst 42 or the DPF 41 of the atertreatment device 40 is completed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst temperature rise control device for an aftertreatment device, and more particularly to an excessive temperature rise of the catalyst after finishing the temperature rise control of the aftertreatment device including an exhaust purification catalyst and a diesel particulate filter (hereinafter referred to as DPF). The present invention relates to a temperature rise control device that prevents the above.

  In order to suppress emission of particulate matter (hereinafter referred to as PM) contained in exhaust gas from a diesel engine, an aftertreatment device including a DPF that collects PM may be provided in the engine exhaust system. In this case, in order to prevent an increase in exhaust pressure due to clogging of the DPF accompanying the collection of PM, a system that burns and removes PM by heating the DPF with an electric heater or a burner, or DPF using exhaust heat from the engine For example, a continuous regeneration type DPF system is used. In this continuous regeneration type DPF system, when PM accumulates more than a threshold value, it is necessary to perform PM regeneration by forced DPF temperature rise. For that purpose, it is necessary to raise the temperature of the DPF to a reproducible temperature and maintain that temperature, and the exhaust gas temperature is necessary for PM regeneration by delaying the fuel injection timing, multistage injection, post injection, injection in the exhaust pipe, etc. The temperature is increased and maintained. However, if the DPF regeneration control is performed under an operating condition with a small amount of exhaust gas during the regeneration of the filter, or under an operating condition with a small amount of exhaust gas, for example, in an idling state, the inside of the DPF becomes a high temperature and there is a problem such as a DPF melting May occur.

Therefore, in the exhaust gas purification system described in Patent Document 1, when the idle operation is determined at the start of the DPF regeneration control operation and during the regeneration control operation, control is performed to increase the idle rotational speed to a predetermined rotational speed, Even during idle operation, an appropriate exhaust gas flow rate is ensured to prevent an excessive temperature rise of the DPF due to a decrease in the exhaust gas flow rate.
JP 2003-161139 A

The exhaust gas purification system described in Patent Document 1 prevents excessive temperature rise of the DPF by idling up during the temperature rise control for DPF regeneration, but the exhaust gas purification system (post-treatment device) provided with the DPF There are various configurations, and depending on the configuration, excessive temperature rise of the exhaust purification catalyst after completion of temperature rise control may be a problem.
For example, even in an aftertreatment device in which a reducing agent such as HC is supplied to the NOx storage catalyst provided in the front stage of the DPF, temperature increase control by HC supply for DPF regeneration and S purge of the NOx storage catalyst It is conceivable to prevent the DPF from overheating by idling up, but in such a configuration, the idling speed is reduced to the normal idling speed when returning to the normal control upon completion of the temperature raising control. Therefore, if the HC supplied to the catalyst remains, the HC remaining in the catalyst is reduced due to a decrease in the inflow of exhaust gas to the catalyst. There is a possibility that the catalyst temperature is excessively increased due to a rapid reaction and the catalyst is deteriorated.

  An object of the present invention is to provide a temperature increase control device that prevents an excessive temperature increase of a catalyst after the temperature increase control of an aftertreatment device is finished.

In order to achieve the above object, according to the first aspect of the present invention, in the temperature increase control device for the aftertreatment device including the exhaust purification catalyst and the DPF, the temperature increase control by the temperature increase control means for regeneration of the catalyst or DPF is completed. Thereafter, the cooling of the catalyst is promoted by the catalyst cooling promoting means until the catalyst temperature detected by the catalyst temperature detecting means becomes equal to or lower than the threshold.
The invention of claim 2 is characterized in that, in the invention of claim 1, the catalyst cooling promoting means maintains the exhaust gas flow rate.

According to a third aspect of the present invention, in the second aspect of the present invention, the catalyst cooling promoting means maintains the idle rotation speed during the temperature rise control.
According to a fourth aspect of the present invention, in any one of the first to third aspects, the catalyst cooling acceleration means is at least one of advance of fuel injection timing, increase of intake air amount, and decrease of EGR amount. The engine combustion control including is performed.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the catalyst cooling promotion means issues a warning to the driver that the engine stop operation is prohibited.

According to the first aspect of the present invention, since the cooling of the catalyst is promoted until the catalyst temperature becomes equal to or lower than the threshold value after the temperature raising control is finished, it is possible to prevent an excessive temperature rise of the catalyst after the temperature raising control is finished. In particular, after the temperature increase control by the supply of HC is completed, the reaction of HC remaining in the catalyst can be suppressed to prevent an excessive temperature increase of the catalyst.
According to the second aspect of the present invention, the exhaust inflow amount to the catalyst is maintained until the catalyst temperature becomes equal to or lower than the threshold value after the temperature rise control is completed. Therefore, the exhaust gas sufficiently flows through the catalyst to promote the cooling of the catalyst, Temperature rise can be prevented.

According to the third aspect of the present invention, the idle rotation speed during the temperature rise control is maintained until the catalyst temperature becomes equal to or lower than the threshold value after the temperature rise control is completed. Therefore, exhaust gas sufficiently flows through the catalyst to promote the cooling of the catalyst. It is possible to prevent an excessive temperature rise.
According to a fourth aspect of the present invention, the engine combustion control includes any one or more of advance of the fuel injection timing, increase of the intake air amount, and decrease of the EGR amount until the catalyst temperature becomes equal to or lower than the threshold value after the temperature increase control is finished. Therefore, one or both of the reduction of the exhaust temperature and the increase of the exhaust flow rate are achieved to promote the cooling of the catalyst, thereby shortening the required cooling time and preventing the catalyst from overheating.

  According to the fifth aspect of the present invention, a warning that the engine stop operation is prohibited is issued to the driver until the catalyst temperature becomes equal to or lower than the threshold value after the temperature rise control is completed. Therefore, the engine stop operation is performed until the catalyst temperature sufficiently decreases. Thus, the driver can be encouraged not to perform the operation to ensure the catalyst cooling time, and the catalyst can be prevented from being overheated.

Hereinafter, with reference to the drawings, a catalyst temperature increase control device of an aftertreatment device according to an embodiment of the present invention will be described.
In FIG. 1, reference numeral 1 indicates an engine, for example, a common rail type diesel engine, and reference numeral 10 indicates an electronic control unit (hereinafter referred to as an ECU) that forms a main part of the engine control device and the temperature raising control device.

  Although not shown in detail, the common rail diesel engine 1 includes, for example, a needle valve and a fuel injector having a fuel chamber and a control chamber provided on the distal end side and the proximal end side of the needle valve for each cylinder. The fuel chamber and the control chamber are connected to the pressure accumulation chamber via a fuel passage, and the control chamber is connected to the fuel tank via a fuel return passage. Under the control of the ECU 10, when the solenoid valve provided in the fuel injector is opened, the high-pressure fuel supplied from the pressure accumulating chamber is injected into the combustion chamber of the engine 1 through the fuel injector, and when the solenoid valve is closed, the fuel injection is finished. Thus, the fuel injection timing can be adjusted by controlling the opening timing of the solenoid valve.

The engine 1 has an intake pipe 12 connected to an intake manifold 11 and an exhaust pipe 14 connected to an exhaust manifold 13.
In the middle of the intake pipe 12, a compressor 21, an intercooler 31, and an intake throttle valve 32 of the supercharger 20 are arranged. The opening degree of the intake throttle valve 32 can be adjusted by the ECU 10 via the intake throttle valve drive unit 33.

On the other hand, in the middle of the exhaust pipe 14, a turbine 22 of the supercharger 20, a light oil addition injector 50, an aftertreatment device 40, and a muffler (not shown) are provided.
The compressor 21 and the turbine 22 of the supercharger 20 are connected so as to be able to rotate synchronously, and the compressor 21 is rotated by the rotational force of the turbine 22 generated by the flow of exhaust gas discharged from the engine 1 and is pressurized by the compressor 21. Intake air is supplied to the engine 1. The air that has been pressurized by the compressor 21 and heated to a high temperature is cooled by the intercooler 31, thereby increasing the density of the intake air and improving the charging efficiency to increase the engine output. The turbocharger 20 is provided with a bypass passage that bypasses the turbine 22. By opening and closing a waste gate 23 provided in the middle of the bypass passage, the amount of exhaust gas passing through the turbine 22 is increased or decreased. By changing the rotation, the pressure of the intake air supplied to the intake pipe 12 can be increased or decreased. The waste gate 23 is opened and closed by the ECU 10 via the waste gate drive unit 24.

  In FIG. 1, reference numeral 36 indicates an EGR passage extending from the exhaust manifold 13 to the intake pipe 12, and a part of the exhaust gas is supplied to the engine 1 as a recirculation gas via the EGR passage 36. In the middle of the EGR passage 36, an EGR cooler 37 that cools the recirculation gas to increase the gas filling density of the engine 1 and an EGR valve 38 for supplying and shutting off the recirculation gas to the engine 1 are provided. ing. The ECU 10 adjusts the opening / closing or opening degree of the EGR valve 38 through the EGR valve drive unit 39.

  The aftertreatment device 40 is for reducing NOx and PM contained in the exhaust gas flowing into the aftertreatment device 40. The post-processing device 40 of the present embodiment is a diesel particulate filter (DPF) 41 that collects PM and burns and removes it, and light oil (HC) that is disposed in front of the DPF 41 and supplied from the light oil addition injector 50 as a reducing agent. And a NOx storage catalyst 42 for purifying NOx in the exhaust gas, and a post-stage catalyst 43 that is disposed downstream of the DPF 41 and oxidizes excess HC and the like.

The light oil addition injector 50 injects light oil (HC) to the NOx storage catalyst 42 and is controlled to be opened and closed by the ECU 10 via the light oil addition injector drive unit 51. The injection amount of light oil from the light oil addition injector 50 is determined based on, for example, the engine speed and the fuel injection amount.
The ECU 10 determines the electromagnetic force of the fuel injectors (not shown) of each cylinder according to the operating range of the engine 1 determined based on the engine load and the engine speed detected by the load sensor and the engine speed sensor (both not shown). The valve is turned on and off to control the fuel injection timing and the fuel injection amount.

In FIG. 1, reference numeral 60 is a catalyst outlet exhaust temperature sensor (catalyst temperature detection means), which has a temperature detection end inserted between the NOx storage catalyst 42 and the DPF 41, on the outlet side of the NOx storage catalyst 42. The exhaust temperature (catalyst temperature in a broad sense) is detected. Reference numeral 70 denotes an alarm device such as an alarm buzzer or an alarm display device driven by the ECU 10.
The diesel engine 1 configured as described above is operated at a lean air-fuel ratio, and during this lean air-fuel ratio operation, NOx (nitrogen oxide) contained in the exhaust gas discharged from the engine 1 is stored in the NOx storage catalyst 42. When the NOx occlusion amount increases to a certain level or more, the rich spike operation of the engine 1 is performed as is known, and the NOx occluded in the NOx occlusion catalyst 42 is released and reduced and removed. Further, if the NOx storage catalyst 42 is poisoned by sulfur due to sulfur contained in the fuel, the exhaust gas purification action of the NOx storage catalyst 42 is reduced, so the S purge that reduces and removes the S component adsorbed on the NOx storage catalyst 42. In order to perform this, conventionally known temperature raising control for raising the exhaust gas temperature (catalyst temperature) such as retarding the fuel injection timing or injecting additional fuel in the latter half of the expansion stroke is performed.

Further, in order to reduce the amount of PM contained in the exhaust gas into the atmosphere, PM is collected by the DPF 41. When the amount of PM collected increases to a certain level or more, the engine is exhausted due to an increase in exhaust pressure due to clogging of the DPF 41. Since there is a possibility that the operation performance is deteriorated, conventionally known temperature increase control is performed in order to regenerate the DPF 41 by burning and removing the collected PM.
In the present embodiment, in the temperature rise control during the S purge of the NOx occlusion catalyst 42 or the regeneration of the DPF 41, the light oil addition injector 50 is opened under the control of the ECU 10 (temperature rise control means), and light oil (HC) is discharged into the exhaust gas. In order to increase the exhaust gas temperature (catalyst temperature) to the target temperature by injecting and thereby increasing the exhaust gas temperature (catalyst temperature), while ensuring the exhaust gas flow rate and preventing the NOx storage catalyst 42 from overheating, The rotation speed is increased by a predetermined number. It should be noted that during the temperature rise control by HC supply, depending on the difference between the actual catalyst temperature detected by the catalyst outlet exhaust temperature sensor 60 (illustrated by a solid line in FIG. 2) and the target temperature (illustrated by a broken line in FIG. 2). Thus, the catalyst temperature can be controlled to the target temperature by correcting the HC supply amount.

The catalyst temperature raising control itself is basically the same as the conventional temperature raising control, but the present invention is characterized in that the cooling of the catalyst is promoted after the temperature raising control is completed.
That is, when the temperature raising control by HC supply is performed at the time of S purge or DPF regeneration, if the normal temperature control is immediately restored upon completion of the temperature raising control, the exhaust flow rate is rapidly reduced and remains in the NOx storage catalyst 42. There is a risk that HC reacts rapidly and the catalyst temperature rapidly rises. FIG. 3 shows changes in the exhaust gas flow rate and the catalyst temperature over time when the idle speed is increased during the temperature increase control and the idle speed is decreased to the normal speed immediately after the temperature increase control is finished. . As shown in FIG. 3, when the idling engine speed is immediately reduced to the normal engine speed from the end of the temperature raising control, the catalyst temperature may excessively increase due to the reaction of the remaining HC with a sudden decrease in the exhaust gas flow rate. , The catalyst deteriorates and the exhaust gas performance is impaired.

  Therefore, in the present invention, under the control of the ECU 10 (catalyst cooling promotion means), the catalyst temperature becomes equal to or lower than a threshold value indicating that the NOx storage catalyst 42 (exhaust purification catalyst) has been sufficiently cooled after the temperature increase control is completed. In order to promote the cooling of the catalyst. More specifically, in this embodiment, the ECU 10 (catalyst cooling acceleration means) monitors the catalyst outlet exhaust temperature detected by the catalyst outlet exhaust temperature sensor 60, that is, the catalyst temperature after the end of the temperature raising control, and this catalyst. Until the temperature becomes equal to or lower than the threshold value indicating that the NOx storage catalyst 42 has been sufficiently cooled, the idle rotation speed during the temperature increase control is maintained even after the temperature increase control is ended by the exhaust flow rate maintaining control, thereby maintaining the exhaust flow rate. Thus, the cooling of the NOx storage catalyst 42 is promoted (see FIG. 2). In addition, said threshold value (temperature reduction threshold value after completion | finish of temperature rising control) is illustrated by the dashed-dotted line in FIG.

  Further, under the control of the ECU 10 (catalyst cooling promoting means), engine combustion control including at least one of advance of the fuel injection timing, increase of the intake air amount, and reduction of the EGR amount is performed. One or both of the reduction of the exhaust gas and the increase of the exhaust gas flow rate are achieved to promote the cooling of the NOx storage catalyst 42. Further, the ECU 10 (catalyst cooling promotion means) drives the alarm device 70 to issue a warning to the driver that the engine stop operation is prohibited. As a result, the driver is urged not to perform an engine stop operation (operation for setting the exhaust gas flow rate to zero) such as ignition key-off, so that the catalyst cooling time is secured and the excessive temperature rise of the NOx storage catalyst 42 is prevented. .

  As described above, after the temperature rise control by the HC supply is completed, the cooling of the NOx storage catalyst 42 is promoted by the exhaust gas inflow by the exhaust flow rate maintenance control, thereby suppressing the reaction of the HC remaining in the NOx storage catalyst 42. When the catalyst temperature detected by the catalyst outlet exhaust temperature sensor 60 falls below the threshold value, the exhaust flow rate maintenance control is terminated and the normal control is resumed (see FIG. 2).

Although the description of the temperature increase control device according to the preferred embodiment of the present invention is finished as above, the present invention is not limited to this and can be variously modified.
For example, in the above-described embodiment, the NOx storage catalyst is used as the exhaust purification catalyst disposed upstream of the DPF, but an oxidation catalyst may be used as the upstream catalyst. Moreover, it is not essential to provide a post-stage catalyst. In the above embodiment, the temperature raising control is performed by supplying HC. However, the temperature raising of the exhaust gas can also be performed by operating intake / exhaust actuators such as an intake throttle valve, an EGR valve, and a turbocharger wastegate. . Further, in order to secure the exhaust flow rate during the temperature raising control, the idle rotation speed is increased in the above embodiment, but other means such as closing the EGR valve may be taken. Further, in the above embodiment, in addition to the exhaust flow rate maintenance control (idle-up maintenance), engine combustion control for realizing reduction of the exhaust temperature and increase of the exhaust flow rate and alarm control for preventing the engine stop operation are performed. However, such control is not essential. The present invention can be modified with respect to points other than those described above.

It is the schematic which shows the temperature rising control apparatus of the post-processing apparatus by one Embodiment of this invention. FIG. 2 is a diagram showing changes in exhaust gas flow rate and catalyst temperature over time during execution of temperature increase control by the temperature increase control device shown in FIG. 1 and subsequent exhaust flow rate maintenance control and normal control. It is a figure which shows the change of the exhaust flow volume and catalyst temperature in the case of returning to normal control with completion | finish of temperature rising control.

Explanation of symbols

1 engine 10 ECU (temperature increase control means, catalyst cooling promotion means)
23 Supercharger wastegate 32 Intake throttle valve 38 EGR valve 40 Exhaust gas aftertreatment device 41 DPF
42 NOx storage catalyst (exhaust gas purification catalyst)
50 Light oil added injector 60 Catalyst outlet exhaust temperature sensor (catalyst temperature detection means)
70 Alarm device

Claims (5)

In a temperature increase control device for an aftertreatment device including an exhaust purification catalyst and a diesel particulate filter,
Catalyst temperature detecting means for detecting the temperature of the exhaust purification catalyst;
Catalyst temperature increase control means for performing temperature increase control during regeneration of the exhaust purification catalyst or the diesel particulate filter;
And a catalyst cooling acceleration means for promoting cooling of the exhaust purification catalyst until the temperature of the exhaust purification catalyst becomes equal to or lower than a threshold value after the temperature increase control is completed.   2. The temperature increase control of the aftertreatment device according to claim 1, wherein the catalyst cooling promotion means maintains the exhaust gas flow rate until the temperature of the exhaust purification catalyst becomes equal to or lower than the threshold value after the temperature increase control is completed. apparatus.   The said catalyst cooling acceleration | stimulation means maintains the idle rotation speed in the said temperature rising control until the temperature of the said exhaust purification catalyst becomes below the said threshold value after completion | finish of the said temperature rising control. Temperature increase control device for the post-processing device.   The catalyst cooling accelerating means includes at least one of advance of the fuel injection timing, increase of the intake air amount, and decrease of the EGR amount until the temperature of the exhaust purification catalyst becomes equal to or lower than the threshold value after completion of the temperature increase control. 4. The temperature increase control device for an aftertreatment device according to claim 1, wherein engine combustion control including one is performed.   The catalyst cooling accelerating means issues a warning for prohibiting the engine stop operation to the driver until the temperature of the exhaust purification catalyst becomes equal to or lower than the threshold value after the temperature increase control is completed. Item 5. A temperature increase control device for a post-processing device according to any one of Items 1 to 4.

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