JP2006105055A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable strict, accurate and fine temperature control in regeneration of DPF. <P>SOLUTION: When it is determined that forced regeneration is necessary based on PM quantity accumulated on DPF 21, post injection is performed in all four cylinders constructing an engine 1 in an early period of temperature rise of exhaust gas based on temperature T of exhaust gas flowing in DPF 21 detected by a temperature sensor 22, and four fuel injection nozzle 3 provided in the cylinders are independently controlled to control number of cylinders in which post injection is performed from maximum 4 to minimum 0 (number of cylinders in which post injection is suspended, from minimum 0 to maximum 4: partial suspension of post injection) when temperature of exhaust gas gets close to target temperature. Consequently additional quantity of un-burnt fuel is strictly, accurately and finely controlled to make temperature of exhaust gas close to the target temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to temperature control when regenerating a diesel particulate filter (DPF).

  Exhaust gas discharged from a diesel engine contains many particulate matter (abbreviated as PM) in addition to HC, CO, NOx, and the like. Thus, diesel particulate filters (abbreviated as DPF) that capture and remove PM and oxidation catalysts that treat HC and CO have been put to practical use as exhaust gas purification devices for diesel engines.

  However, the temperature of exhaust gas is relatively low in a diesel engine, and in normal operation, the temperature of the DPF does not increase so much that the PM burns. Further, when the DPF is installed at a position away from the engine, the exhaust gas is cooled in the exhaust passage, and the heat of the exhaust gas cannot be used effectively.

  In this way, under the condition where the temperature of the DPF is low, the PM deposited on the DPF is not sufficiently regenerated, so the accumulation amount usually increases. When the PM accumulation amount increases, the filter pressure loss of the DPF increases. There is a problem that the exhaust pressure increases due to the increase and causes a pumping loss and the like, resulting in deterioration of fuel consumption and exhaust gas. Further, in a state where PM is excessively accumulated on the filter, the filter may be damaged if the PM self-ignites during high load operation or the like.

  Therefore, in order to prevent these fears, when the time to remove the PM trapped in the DPF is reached, forced regeneration is performed to forcibly remove the PM. As a method of forced regeneration, for example, there is a post-injection technique in which, after supplying fuel for main combustion, additional fuel is supplied into the cylinder in an expansion stroke or an exhaust stroke.

  In this forced regeneration by post-injection, when post-injection is first performed in a relatively early expansion stroke, the additional fuel is combined with surplus oxygen and burned to raise the exhaust temperature. This raises the temperature of the oxidation catalyst. When the oxidation catalyst is heated and activated, the additional fuel injected in the later stage of the expansion stroke or in the exhaust stroke is oxidized by the oxidation catalyst, and the PM on the DPF is forcibly and favorably removed by the oxidation heat. (See Patent Document 1 below).

JP 2003-3829 A

  However, when considering a control system in which the amount of additional fuel added is input and the exhaust gas temperature at the outlet of the oxidation catalyst is output, the control system has a slow input / output response characteristic due to the large heat capacity of the oxidation catalyst. Therefore, strict, accurate, and delicate addition fuel addition control is required. For example, when the overshoot amount of the control temperature of the exhaust gas increases, the PM accumulated on the DPF burns rapidly, and as a result, the DPF may be damaged beyond the heat resistant temperature.

  The injector driver and the injector body that inject additional fuel have an injection lower limit, and the conventional post-injection control does not perform strict, precise, and delicate fuel injection control, resulting in exhaust gas temperature control. There was a limit to control accuracy.

  The exhaust gas flowing into the oxidation catalyst is heated by oxidizing the unburned fuel by post injection in the oxidation catalyst, and the PM accumulated in the DPF is forcibly regenerated by the heated exhaust gas. . However, since delicate fuel injection control is not performed, the temperature of the exhaust gas at the inlet and outlet of the DPF is unstable, and there is a risk of DPF damage.

  The present invention has been made in view of the above situation, and relates to an exhaust gas purification apparatus for an internal combustion engine, and in particular, temperature control when regenerating a diesel particulate filter (DPF) can be performed precisely, accurately, and delicately. It is an object to provide a simple device.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention that solves the above problems
A filter that is provided in an exhaust passage of the internal combustion engine and collects particulates in the exhaust gas;
An oxidation catalyst provided in the exhaust passage located upstream of the filter;
When regeneration of the filter is required, a filter regeneration means for regenerating the filter is added by adding fuel by post-injection, reacting the added fuel with the oxidation catalyst, and raising the temperature of the filter. Prepared,
The filter regeneration means is characterized in that the post-injection is partially stopped when the required temperature rise is reduced.

  The degree of temperature rise of the filter varies from a large degree of temperature rise to a slight degree of temperature rise, and the amount of unburned fuel added by post injection is adjusted to cope with this, but this adjustment performs post injection. Limited by the injection lower limit of the injector driver and injector body. Therefore, when the addition amount adjustment of the unburned fuel is performed in a very small amount range, the addition amount adjustment in the very small amount range is performed by partially stopping the post injection (adding only by the post injection that does not stop).

In the exhaust gas purification apparatus for an internal combustion engine,
Exhaust gas temperature detection means for detecting the temperature of the exhaust gas flowing into the filter,
The filter regeneration means changes the rate at which the post-injection is stopped according to the difference between the exhaust gas temperature detected by the exhaust gas temperature detection means and the target temperature, so that the temperature of the exhaust gas becomes the target temperature. Control is performed so as to approach the temperature.

  By controlling the amount of unburned fuel added in the vicinity of the target temperature delicately, the temperature of the filter is precisely controlled.

In the exhaust gas purification apparatus for an internal combustion engine,
The filter regeneration means is characterized in that the post injection is partially stopped by changing a ratio between the number of cylinders that perform post injection and the number of cylinders that stop post injection.

  Rather than adjusting the addition amount based on the assumption that post injection is performed in all cylinders constituting the internal combustion engine, the post injection is partially controlled by controlling the presence or absence of the post injection and the addition amount independently for each cylinder. Try to pause.

In the exhaust gas purification apparatus for an internal combustion engine,
The filter regeneration means is characterized in that the post injection is partially stopped by changing a ratio between the number of cycles for performing the post injection and the number of cycles for stopping the post injection.

  Rather than adjusting the amount of addition based on the assumption that the internal combustion engine performs post-injection in every combustion cycle, post-injection is partially controlled by controlling the presence or absence of post-injection and the amount of addition independently for each cycle. Try to pause.

According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention,
A filter that is provided in an exhaust passage of the internal combustion engine and collects particulates in the exhaust gas;
An oxidation catalyst provided in the exhaust passage located upstream of the filter;
When regeneration of the filter is required, a filter regeneration means for regenerating the filter is added by adding fuel by post-injection, reacting the added fuel with the oxidation catalyst, and raising the temperature of the filter. Prepared,
Since the filter regeneration means partially stops the post-injection when the required temperature rise decreases,
Even in a situation where the required amount of added fuel is small, the amount of fuel added can be accurately controlled. As a result, excessive temperature rise of the filter can be reliably prevented, and the control accuracy of the filter temperature is improved. Further, it is not necessary to use a high-precision injector that is designed to have a very low injection lower limit for the injection amount per injection of the fuel injector, and the cost can be reduced.

In the exhaust gas purification apparatus for an internal combustion engine,
Exhaust gas temperature detection means for detecting the temperature of the exhaust gas flowing into the filter,
The filter regeneration means changes the rate at which the post-injection is stopped according to the difference between the exhaust gas temperature detected by the exhaust gas temperature detection means and the target temperature, so that the temperature of the exhaust gas becomes the target temperature. Since it was controlled to approach the temperature,
The filter temperature can be efficiently maintained near the target temperature, and the filter can be efficiently regenerated.

In the exhaust gas purification apparatus for an internal combustion engine,
Since the filter regeneration means is configured to partially pause the post injection by changing the ratio of the number of cylinders that perform post injection and the number of cylinders that stop post injection.
With relatively simple control, stable filter temperature control can be realized.

In the exhaust gas purification apparatus for an internal combustion engine,
Since the filter regeneration means is configured to partially pause the post injection by changing the ratio between the number of cycles for performing post injection and the number of cycles for stopping post injection.
The amount of added fuel can be controlled with high accuracy, and the filter temperature can be controlled with higher accuracy.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, the following embodiments do not limit the present invention. FIG. 1 is a schematic configuration diagram illustrating an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention.

  As shown in FIG. 1, an engine 1 that is an internal combustion engine is, for example, a common rail in-line four-cylinder diesel engine. In the common rail engine 1, an electromagnetic fuel injection nozzle 3 is provided in each cylinder facing the combustion chamber 2, and each fuel injection nozzle 3 is connected to a common rail 5 by a high-pressure pipe 4. The common rail 5 is connected to the fuel tank 8 via a high-pressure pipe 6 in which a high-pressure pump 7 is interposed. Since engine 1 is a diesel engine, light oil is used as the fuel.

  An electromagnetic intake throttle valve 10 is provided in the intake passage 9 of the engine 1. An EGR passage 13 extends from the upstream portion of the exhaust passage 12, and the end of the EGR passage 13 is connected to a portion of the intake passage 9 downstream of the intake throttle valve 10. An electromagnetic EGR valve 14 is interposed in the EGR passage 13.

Further, an exhaust purification device is interposed in the downstream portion of the exhaust passage 12. The exhaust emission control device is configured by providing an oxidation catalyst (DOC) 20 upstream of a diesel particulate filter (DPF) 21. The exhaust purification device is configured to generate an oxidant (NO ₂ ) in the oxidation catalyst 20 and continuously oxidize and remove particulate matter (PM) deposited on the downstream DPF 21 by the generated oxidant. ing.

  On the input side of the electronic controller (ECU) 15 are an air flow sensor 11 for detecting the intake air amount Qa, a temperature sensor 22 for detecting the exhaust gas temperature upstream of the DPF 21 and downstream of the oxidation catalyst 20, and depression of the accelerator pedal 16. Various sensors such as an accelerator opening sensor 17 for detecting the amount, that is, the accelerator opening θacc, are connected, and on the output side, various kinds of fuel injection nozzle 3, high pressure pump 7, intake throttle valve 10, EGR valve 14, and the like. Devices are connected.

  Thereby, various devices are controlled based on various input information, and the engine 1 is appropriately controlled. In addition, the exhaust gas purification apparatus for an internal combustion engine according to the present invention forcibly removes (forcibly regenerates) the PM trapped in the DPF 21, after performing main injection for main combustion by the fuel injection nozzle 3, The fuel injection nozzle 3 is configured so that additional supply of fuel, that is, post injection, can be performed in the expansion stroke or exhaust stroke.

  As a result, when the DPF 21 cannot perform the continuous regeneration function under normal operating conditions, the oxidation reaction between unburned fuel (HC, CO, etc.) by post injection and oxygen in the exhaust is performed on the oxidation catalyst 20. It is possible to activate the oxidation catalyst 20 by accelerating, and to raise the temperature of the DPF 21 by the heat of this oxidation reaction, and forcibly remove the PM deposited on the DPF 21 by combustion.

  In the present invention, the post injection performed by the fuel injection nozzle 3 is partially stopped in a predetermined case. This is because the control of the amount of unburned fuel added by post injection requires strict, precise, and delicate control. As an example of partially suspending the post injection, the first and second embodiments will be described in detail below.

<First Embodiment>
A first embodiment will be described with reference to FIGS. FIG. 2 is a graph showing the exhaust gas temperature control method and the controlled exhaust gas temperature in the exhaust gas purification apparatus according to the first embodiment. FIG. 3 is a flowchart showing the exhaust gas temperature control method in the exhaust gas purification apparatus according to the first embodiment.

  In the present embodiment, the post injection is partially stopped by changing the ratio between the number of cylinders that perform post injection and the number of cylinders that stop post injection. As shown in FIG. 2A, the exhaust gas (about 250 degrees) flowing into the oxidation catalyst 20 is heated by the oxidation heat of unburned fuel by post injection in the oxidation catalyst 20, and flows into the downstream DPF 21. In some cases, the exhaust gas is about 600 to 700 ° C. The PM exhausted on the DPF 21 is forcibly regenerated by the exhaust gas whose temperature has been raised.

  The forced regeneration is preferably controlled to about 600 to 700 ° C., for example, from the relationship with the heat resistance temperature of the DPF 21 and the combustion temperature of PM. Therefore, as shown in FIG. 2B, post-injection is performed in all four cylinders at the initial stage of exhaust gas temperature rise (exhaust gas temperature is about 600 ° C. or lower), but the exhaust gas temperature is about 600 ° C. or higher. When it becomes, it controls so that the number of cylinders which perform post-injection is changed and it approaches target temperature.

  In other words, a total of four fuel injection nozzles 3 provided in each of the four cylinders constituting the engine 1 are independently controlled so that the number of cylinders that perform post-injection is increased from a maximum of 4 to a minimum of 0 (a cylinder that stops post-injection). Is controlled so that the post-injection is partially stopped), the amount of unburned fuel added can be controlled strictly, accurately, and delicately.

  Since the conventional control of the amount of unburned fuel added by post injection does not independently control the fuel injection nozzles provided in each cylinder, for example, the minimum amount of unburned fuel added per fuel injection nozzle This is the total number of cylinders over which the minimum injection amount is applied, and the addition amount was set to zero when trying to reduce the addition amount below this. In addition, when trying to increase the addition amount, the addition amount is controlled with the total number of cylinders as one unit. For this reason, strict, accurate, and delicate fuel injection control is not performed, and the control accuracy of exhaust gas temperature control is limited.

  In the present embodiment, for example, as shown in FIG. 3A, T1 lower by a predetermined temperature and T4 higher by a predetermined temperature than the target temperature are set. Further, T2 and T3 that are closer to the target temperature are set. Then, by comparing these set temperatures with the actual exhaust gas temperature, post injection control is performed to control the exhaust gas temperature. An exhaust gas temperature control method will be described based on the flowchart shown in FIG.

  When it is determined from the amount of PM accumulated in the DPF 21 that forced regeneration is necessary, post injection control is performed based on the temperature T of the exhaust gas flowing into the DPF 21 detected by the temperature sensor 22. If it is determined in step S31 that the exhaust gas temperature T is equal to or lower than the set value T1, the exhaust gas temperature T is still low. Therefore, in step S35, control is performed so that post injection is performed in all four cylinders. If it is determined in step S31 that the exhaust gas temperature T is higher than the set value T1, the process proceeds to step S32.

  In step S32, when it is determined that the exhaust gas temperature T is higher than the set value T1 and lower than the set value T2, the exhaust gas temperature T has approached the target temperature. Control is performed so that post injection is performed in one cylinder (post injection in one cylinder is stopped). If it is determined in step S32 that the exhaust gas temperature T is higher than the set value T2, the process proceeds to step S33.

  If it is determined in step S33 that the exhaust gas temperature T is higher than the set value T2 and lower than or equal to the set value T3, the exhaust gas temperature T is close to the target temperature. Control is performed so that post injection is performed in one cylinder (post injection in two cylinders is stopped). If it is determined in step S33 that the exhaust gas temperature T is higher than the set value T3, the process proceeds to step S34.

  The reason why the post-injection is not completely stopped immediately after the temperature becomes higher than the target temperature (target temperature <T ≦ T3) is, for example, for the purpose of keeping the exhaust gas temperature. The post-injection may be completely stopped when the temperature becomes higher than the temperature.

  In step S34, if it is determined that the exhaust gas temperature T is higher than the set value T3 and lower than the set value T4, the exhaust gas temperature T is moving away from the target temperature. Control is performed so that post injection is performed in one cylinder (post injection in three cylinders is stopped).

  If it is determined in step S34 that the exhaust gas temperature T is higher than the set value T4, the exhaust gas temperature T is already high, so the process proceeds to step S39 and post-injection for all four cylinders is stopped.

  In this way, a total of four fuel injection nozzles 3 provided in each of the four cylinders are independently controlled, and the number of cylinders that perform post injection is a maximum of four according to the difference between the exhaust gas temperature and the target temperature. Therefore, the temperature of the exhaust gas flowing into the DPF 21 can be controlled precisely, accurately, and delicately by controlling so that the number of cylinders that stop post-injection becomes 0 (minimum 0 to maximum 4).

  The above description is an example of cylinder number control for performing post injection based on the exhaust gas temperature T, and other factors such as the exhaust gas flow rate are taken into consideration, and the post is taken into consideration with these factors. The number of cylinders to be injected may be changed.

<Second Embodiment>
A second embodiment will be described with reference to FIGS. FIG. 4 is a graph showing the exhaust gas temperature control method and the controlled exhaust gas temperature in the exhaust gas purification apparatus according to the second embodiment. FIG. 5 is a flowchart showing a method for controlling the temperature of exhaust gas in the exhaust gas purification apparatus according to the second embodiment.

  In this embodiment, the post-injection is partially paused by changing the ratio between the number of cycles in which the post-injection is performed and the number of cycles in which the post-injection is paused. As shown in FIG. 4A, the exhaust gas (about 250 degrees) flowing into the oxidation catalyst 20 is heated by the oxidation heat of the unburned fuel by post injection in the oxidation catalyst 20, and flows into the downstream DPF 21. In some cases, the exhaust gas is about 600 to 700 ° C. The PM exhausted on the DPF 21 is forcibly regenerated by the exhaust gas whose temperature has been raised.

  The forced regeneration is preferably controlled to about 600 to 700 ° C., for example, from the relationship with the heat resistance temperature of the DPF 21 and the combustion temperature of PM. Therefore, as shown in FIG. 4B, at the initial stage of exhaust gas temperature rise (the exhaust gas temperature is about 600 ° C. or less), the ratio of the cycle in which the post injection is performed is set to 100%. When the temperature is 600 ° C. or higher, control is performed so as to approach the target temperature by changing the ratio of the cycle in which the post injection is performed.

  Here, "one cycle" means a series of one repetition consisting of an intake stroke, a compression stroke, a combustion / expansion stroke, and an exhaust stroke in one cylinder. For example, by performing post-injection in any one of the four cycles and suspending post-injection in the remaining three cycles, the proportion of cycles for post-injection is 25%. Further, for example, by performing post injection in any one of the 20 cycles and stopping the post injection in the remaining 19 cycles, the ratio of the cycles of post injection becomes 5%.

  In this way, the ratio of the number of cycles in which post injection is performed and the number of cycles in which post injection is suspended is controlled by independently controlling a total of four fuel injection nozzles 3 provided in each of the four cylinders constituting the engine 1. By changing the ratio, it is possible to finely control the ratio of the post-injection cycle between 0% and 100%, and the amount of unburned fuel added is more strict, accurate, and delicate than in the first embodiment. To be able to control.

  In the present embodiment, for example, as shown in FIG. 5A, T1 lower by a predetermined temperature and T2 higher by a predetermined temperature are set with respect to the set target temperature. Then, by comparing these set temperatures with the actual exhaust gas temperature, post injection control is performed to control the exhaust gas temperature. An exhaust gas temperature control method will be described based on the flowchart shown in FIG. 5B and the exhaust gas temperature-injection cycle ratio map shown in FIG.

  When it is determined from the amount of PM accumulated in the DPF 21 that forced regeneration is necessary, post injection control is performed based on the temperature T of the exhaust gas flowing into the DPF 21 detected by the temperature sensor 22. If it is determined in step S51 that the exhaust gas temperature T is equal to or lower than the set value T1, the exhaust gas temperature T is still low, so that the post-injection cycle ratio is controlled to 100% in step S53. To do. If it is determined in step S51 that the exhaust gas temperature T is higher than the set value T1, the process proceeds to step S52.

  In step S52, if it is determined that the exhaust gas temperature T is higher than the set value T1 and lower than the set value T2, the exhaust gas temperature T is close to the target temperature, so in step S54 the exhaust gas temperature-injection cycle. The post injection is controlled based on the ratio map (FIG. 5C). If it is determined in step S52 that the exhaust gas temperature T is higher than the set value T2, the exhaust gas temperature T is already high. Therefore, the process proceeds to step S55, and the ratio of the post injection cycle is set to 0%. Control.

  The post injection control based on the exhaust gas temperature-injection cycle ratio map shown in FIG. 5C is performed when the exhaust gas temperature T is in the temperature range from T1 to T2, as shown in FIG. The post-injection cycle rate is gradually decreased from 100% to 0% according to the temperature T.

  In this way, a total of four fuel injection nozzles 3 provided in each of the four cylinders are independently controlled, and the number of cycles for performing the post injection and the post injection are determined according to the difference between the exhaust gas temperature and the target temperature. By changing the ratio with the number of cycles to pause, the temperature of the exhaust gas flowing into the DPF 21 can be controlled precisely, accurately and delicately.

  The above description is an example of cycle ratio control for performing post injection based on the exhaust gas temperature T, and other factors such as the exhaust gas flow rate are taken into account, and the post is taken into account. The cycle ratio to be injected may be changed instead of the linear map as shown in FIG.

  In each of the above-described embodiments, the example in which the exhaust gas temperature is controlled only by the post injection control has been described. However, in addition to the post injection control, for example, the exhaust gas is controlled by controlling the amount of oxygen supplied to the oxidation catalyst 20. The temperature may be controlled. The oxygen amount is controlled, for example, by feedback control of the intake throttle valve 10 and the EGR valve 14 so that the air amount detected by the air flow sensor 11 becomes the target air amount.

1 is a schematic configuration diagram showing an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the temperature control method of the exhaust gas in the exhaust gas purification apparatus which concerns on 1st Embodiment, and the temperature of the controlled exhaust gas. It is a flowchart which shows the temperature control method of the exhaust gas in the exhaust gas purification apparatus which concerns on 1st Embodiment. It is a graph which shows the temperature control method of the exhaust gas in the exhaust gas purification apparatus which concerns on 2nd Embodiment, and the temperature of the controlled exhaust gas. It is a flowchart which shows the temperature control method of the exhaust gas in the exhaust gas purification apparatus which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Combustion chamber 3 Fuel injection nozzle 4 High pressure pipe 5 Common rail 6 High pressure pipe 7 High pressure pump 8 Fuel tank 9 Intake passage 10 Intake throttle valve 11 Air flow sensor 12 Exhaust passage 13 EGR passage 14 EGR valve 15 Electronic controller (ECU)
16 Accelerator pedal 17 Accelerator opening sensor 20 Oxidation catalyst (DOC)
21 Diesel particulate filter (DPF)
22 Temperature sensor

Claims (4)

A filter that is provided in an exhaust passage of the internal combustion engine and collects particulates in the exhaust gas;
An oxidation catalyst provided in the exhaust passage located upstream of the filter;
When regeneration of the filter is required, a filter regeneration means for regenerating the filter is added by adding fuel by post-injection, reacting the added fuel with the oxidation catalyst, and raising the temperature of the filter. Prepared,
The exhaust gas purification apparatus for an internal combustion engine, wherein the filter regeneration means partially stops the post-injection when a required temperature rise is reduced. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
Exhaust gas temperature detection means for detecting the temperature of the exhaust gas flowing into the filter,
The filter regeneration means changes the rate at which the post-injection is stopped according to the difference between the exhaust gas temperature detected by the exhaust gas temperature detection means and the target temperature, so that the temperature of the exhaust gas becomes the target temperature. An exhaust purification device for an internal combustion engine, which is controlled so as to approach a temperature. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The filter regeneration means partially stops the post-injection by changing a ratio between the number of cylinders that perform post-injection and the number of cylinders that stop post-injection. Purification equipment. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the filter regeneration means partially stops the post injection by changing a ratio between the number of cycles for performing the post injection and the number of cycles for stopping the post injection. .

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