JP2007002774A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress degradation in exhaust emission when executing regeneration control for regenerating the exhaust emission control capability of an exhaust emission control device provided in an exhaust passage in an exhaust emission control system for an internal combustion engine. <P>SOLUTION: A rate of a temperature change of inflow exhaust when starting regeneration control is calculated. When the rate of the temperature change is a negative value and comparatively low, the quantity of a reducing agent supplied to a catalyst in the initial phase of regeneration control is set smaller in comparison with the case that the rate of the temperature change is comparatively high. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine including an exhaust gas purification device provided in an exhaust passage of the internal combustion engine and a catalyst having an oxidation function provided in an exhaust gas passage upstream of the exhaust gas purification device.

  An exhaust purification system for an internal combustion engine includes an exhaust purification device provided in an exhaust passage of the internal combustion engine, and a catalyst having an oxidation function provided in an exhaust passage upstream of the exhaust purification device. It has been. Here, examples of the exhaust purification device include a particulate filter (hereinafter simply referred to as a filter) carrying a catalyst having an oxidation function and an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst). The filter collects particulate matter (hereinafter referred to as PM) in the exhaust. Further, the NOx catalyst occludes NOx when the surrounding atmosphere is an oxidizing atmosphere, and reduces NOx occluded when the reducing atmosphere is a reducing atmosphere.

  In such an exhaust purification system for an internal combustion engine, regeneration control is performed to regenerate the exhaust purification capability of the exhaust purification device. In this regeneration control, the temperature of the exhaust purification device is raised. As a method of raising the temperature at this time, a method of supplying a reducing agent to a catalyst having an oxidation function provided on the upstream side of the exhaust purification device is known. In such a method, the temperature of the exhaust gas flowing into the exhaust purification device (hereinafter referred to as inflowing exhaust gas) rises due to oxidation heat generated by oxidizing the reducing agent in the catalyst. Then, the exhaust purification device rises in temperature as the inflowing exhaust gas rises.

Patent Document 1 discloses a technique for controlling the amount of reducing agent supplied to the catalyst based on the temperature of the inflowing exhaust gas in the regeneration control as described above.
JP 2003-83029 A JP 2001-227381 A Japanese Patent Laid-Open No. 7-97918

  In the regeneration control, when the reducing agent is supplied to the catalyst having an oxidation function provided on the upstream side of the exhaust purification device, if the reducing agent supply amount is excessive with respect to the temperature of the catalyst, a part of the reducing agent is There is a possibility that exhaust emission is deteriorated by being discharged outside without being oxidized by the catalyst. Therefore, it is necessary to control the supply amount of the reducing agent according to the temperature of the catalyst.

  However, it is difficult to directly detect the temperature of the catalyst. Therefore, the reducing agent supply amount may be controlled in accordance with the temperature of the exhaust downstream of the catalyst, that is, the temperature of the inflowing exhaust. In such a case, there is a difference between the temperature of the catalyst and the temperature of the inflowing exhaust gas, which may result in an excessive amount of reducing agent supply.

  The present invention has been made in view of the above-described problems, and provides a technique capable of suppressing deterioration of exhaust emission during execution of regeneration control in an exhaust purification system of an internal combustion engine. Let it be an issue.

The present invention relates to an exhaust purification system for an internal combustion engine including an exhaust purification device and a catalyst having an oxidation function provided in an exhaust passage upstream of the exhaust purification device. Calculate the temperature change rate of the exhaust. When the temperature change rate is a negative value, the reducing agent to the catalyst at the initial stage of the regeneration control when the exhaust temperature change rate is relatively small compared to when the exhaust temperature change rate is relatively large. Reduce the amount supplied.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
An exhaust purification device provided in the exhaust passage of the internal combustion engine;
A catalyst having an oxidation function provided in the exhaust passage upstream of the exhaust purification device;
Inflow exhaust gas temperature detection means for detecting the temperature of inflow exhaust gas that is exhaust gas flowing into the exhaust gas purification device;
An exhaust gas temperature change rate calculating means for calculating an exhaust gas temperature change rate that is a change amount per unit time of the temperature of the inflowing exhaust gas;
Regeneration control execution means for performing regeneration control for increasing the temperature of the exhaust purification device by supplying a reducing agent to the catalyst from the upstream side thereof, thereby regenerating the exhaust purification capability of the exhaust purification device;
A reducing agent supply amount determining means for determining a reducing agent supply amount to the catalyst in the regeneration control,
The regeneration control execution means starts the regeneration control when a predetermined condition is satisfied,
The reducing agent supply amount determining means calculates a reference supply amount that is a reference value of the reducing agent supply amount to the catalyst in the regeneration control based on the intake air amount of the internal combustion engine and the temperature of the inflowing exhaust gas. And when the exhaust temperature change rate when the predetermined condition is satisfied is a negative value, the exhaust temperature change rate is compared when the exhaust temperature change rate is relatively small. The reference supply amount is corrected so as to be smaller than when it is large, and the correction amount is set as an initial supply amount that is a reducing agent supply amount to the catalyst at the initial stage of execution of the regeneration control.

  Here, the predetermined condition is a condition where it can be determined that it is necessary to regenerate the exhaust purification capability of the exhaust purification device. This predetermined condition is predetermined.

  In the regeneration control according to the present invention, a reducing agent is supplied to the catalyst from the upstream side. As the reducing agent is oxidized by the catalyst, the inflowing exhaust gas is heated. Along with this, the temperature of the exhaust purification device is raised.

  The reducing agent supply amount to the catalyst in this regeneration control is determined by the reducing agent supply amount determining means. The reducing agent supply amount determination means has reference supply amount calculation means, and the reference supply amount calculation means calculates the reference supply amount based on the intake air amount of the internal combustion engine and the temperature of the inflowing exhaust gas.

  When the temperature of exhaust gas discharged from the internal combustion engine (hereinafter referred to as engine exhaust gas) decreases due to a change in the operating state of the internal combustion engine, the temperature of the catalyst and inflowing exhaust gas also decreases accordingly. At this time, since the catalyst has a heat capacity, the temperature of the catalyst gradually decreases from the upstream portion along the flow of the exhaust gas. For this reason, the temperature of the downstream part of the catalyst may be higher than the temperature of the upstream part and the central part of the catalyst until a sufficient time elapses after the temperature of the engine exhaust gas starts to decrease. Even if the temperatures of the upstream and central portions of the catalyst are relatively low, the exhaust gas passing through the catalyst is heated by the downstream portion of the catalyst while the temperature of the downstream portion of the catalyst is relatively high. Is done. As a result, the temperature decrease of the inflowing exhaust gas is delayed from the temperature decrease of the upstream portion and the middle flow portion of the catalyst.

  That is, when the temperature of the engine exhaust exhaust gas decreases, the temperature of the inflow exhaust gas may be higher than the temperatures of the upstream and middle flow portions of the catalyst until a sufficient time has elapsed. In such a state, when the regeneration control is executed and the reference supply amount of the reducing agent calculated based on the intake air amount and the temperature of the inflowing exhaust gas is supplied to the catalyst, the reducing agent supply amount becomes the actual amount. The amount is excessive with respect to the temperature of the catalyst.

  Further, when the temperature of the inflowing exhaust gas is lowered, the exhaust gas temperature change rate calculated by the exhaust gas temperature change rate calculating means becomes a negative value. Here, as described above, the temperature decrease of the inflowing exhaust gas is delayed from the temperature decrease of the upstream portion and the central portion of the catalyst. That is, when the exhaust gas temperature change rate is a negative value, it can be determined that the upstream and central temperatures of the catalyst are further lower than the temperature of the inflowing exhaust gas.

  Further, when the temperature of the catalyst decreases due to a decrease in the temperature of the engine exhaust exhaust, the temperature decrease amount per unit time of the catalyst becomes smaller as time elapses from the time when the temperature of the catalyst starts to decrease. . And since the temperature of the inflowing exhaust gas changes in the same way as the temperature of the catalyst, when the exhaust gas temperature change rate is a negative value, the exhaust gas temperature change rate increases as time elapses from the time when the temperature of the inflowing exhaust gas starts to decrease. It becomes a large value (the absolute value of the exhaust gas temperature change rate becomes small). Further, as time elapses from the time when the temperature of the inflowing exhaust gas starts to decrease, the temperature difference between the inflowing exhaust gas and the upstream and downstream portions of the catalyst becomes smaller.

  That is, when the exhaust gas temperature change rate at the time when the predetermined condition is satisfied is a negative value, the temperature of the inflowing exhaust gas is higher than the temperatures of the upstream and central portions of the catalyst at that time, and The smaller the exhaust gas temperature change rate (the greater the exhaust gas temperature change rate), the greater the temperature difference between the inflowing exhaust gas and the upstream and central parts of the catalyst.

  Therefore, in the present invention, when the exhaust temperature change rate when the predetermined condition is satisfied is a negative value, when the exhaust temperature change rate is relatively small, compared to when the exhaust temperature change rate is relatively large. Correct so that the reference supply amount is smaller. The correction amount is set as an initial supply amount that is a reducing agent supply amount at the initial stage of the regeneration control.

  Here, the initial execution of the regeneration control may be at the start of the supply of the reducing agent to the catalyst, and the period from the start of the supply of the reducing agent to the catalyst until the temperature of the inflowing exhaust gas starts to rise. May be good.

  In the control as described above, when the temperature of the inflowing exhaust gas is higher than the temperatures of the upstream and central portions of the catalyst at the start of the regeneration control, when the temperature difference is relatively large, that is, the upstream portion of the catalyst and When the temperature of the central portion is relatively low, the initial supply amount in the regeneration control is small compared to when the temperatures of the upstream portion and the central portion of the catalyst are relatively high. Therefore, it can suppress that a reducing agent supply quantity becomes an excessive quantity with respect to the temperature of a catalyst.

  Therefore, according to the present invention, it is possible to suppress the deterioration of exhaust emission when the regeneration control is executed. Moreover, when the fuel of an internal combustion engine is used as a reducing agent, the deterioration of fuel consumption can also be suppressed.

  In the present invention, when the operation state of the internal combustion engine becomes a transient operation state in which the load and the rotational speed are reduced, from the time when the temperature of the engine exhaust exhaust begins to decrease to the time when the temperature of the inflow exhaust begins to decrease. There may be further provided a temperature decrease delay time calculating means for calculating a temperature decrease delay time which is a period of the above.

  When the operation state of the internal combustion engine becomes a transient operation state in which the load and the rotational speed are reduced, the temperature of the engine exhaust gas is lowered. When the temperature of the engine exhaust exhaust begins to decrease, the temperature of the inflow exhaust begins to decrease with a delay. The temperature decrease delay time calculating means calculates the temperature decrease delay time at this time.

The temperature decrease delay time becomes longer as the amount of heat of the catalyst at the time when the operation state of the internal combustion engine becomes the transient operation state as described above increases. Further, the larger the intake air amount when the operating state of the internal combustion engine is in the transient operating state as described above, the more the intake air is taken away from the catalyst by the exhaust while the operating state of the internal combustion engine is in the transient operating state. The amount of heat increases. Therefore, the temperature decrease delay time becomes shorter as the intake air amount increases when the operating state of the internal combustion engine becomes the transient operation state as described above.

  Further, when the exhaust gas temperature change rate is a negative value, the temperature of the inflowing exhaust gas is decreasing. In such a case, when regeneration control is executed and the temperature of the engine exhaust exhaust gas rises, the temperature of the inflow exhaust gas starts to rise accordingly. However, in this case, the temperature of the inflowing exhaust gas rises with a delay in the temperature rise of the engine exhaust exhaust gas, as in the case where the temperature of the engine exhaust exhaust gas decreases. That is, the temperature of the inflowing exhaust gas starts to rise after a certain delay after the temperature of the engine exhaust exhaust gas starts to rise.

  Further, in such a case, a period from the time when the temperature of the engine exhaust gas starts to rise to the time when the temperature of the inflow exhaust gas starts to rise (hereinafter referred to as a temperature rise delay period) The time is substantially the same as the temperature decrease delay time in the transient operation state as described above. That is, the shorter the temperature decrease delay time, the shorter the temperature increase delay time.

  On the other hand, when the regeneration control is started, the temperature of the upstream portion and the central portion of the catalyst starts to rise relatively quickly as the engine exhaust gas is heated.

  Therefore, when the predetermined condition is satisfied after the operation state of the internal combustion engine becomes a transient operation state in which the load and the rotational speed decrease, the exhaust gas temperature change rate at the time when the predetermined condition is satisfied is a negative value Even if the reducing agent supply amount at the start of the supply of the reducing agent to the catalyst is used as the initial supply amount as described above, the regeneration control is started, and the reducing agent supply amount may be gradually increased after starting the reducing agent supply. good.

  Furthermore, when the temperature of the inflowing exhaust gas starts to rise after the start of the regeneration control, the temperature of the inflowing exhaust gas and the upstream and central portions of the catalyst are substantially the same. For this reason, at the start of the temperature rise of the inflowing exhaust gas, it is unlikely that the reducing agent supply amount will be excessive even if the reducing agent supply amount is increased to the reference supply amount. Therefore, the shorter the temperature rise delay time of the inflowing exhaust gas, the faster the reducing agent supply amount can be increased from the initial supply amount to the reference supply amount. As described above, the shorter the temperature decrease delay time, the shorter the temperature increase delay time.

  Therefore, as described above, the regeneration control is started with the reducing agent supply amount at the start of the reducing agent supply to the catalyst as the initial supply amount, and when the reducing agent supply amount is gradually increased after starting the reducing agent supply, The increase rate may be increased as the temperature decrease delay time calculated by the temperature decrease delay time calculation means is shorter.

  According to this, after the start of the regeneration control, the shorter the time until the temperature of the inflowing exhaust gas starts to rise, that is, the time until the temperature of the inflowing exhaust gas and the upstream and central portions of the catalyst reach substantially the same temperature. The amount of reducing agent supplied to the catalyst is increased more rapidly. Therefore, in the regeneration control, it is possible to supply more reducing agent to the catalyst while suppressing an excessive amount of reducing agent from being supplied to the catalyst. Accordingly, it is possible to raise the temperature of the exhaust purification device more quickly while suppressing the deterioration of exhaust emission.

  With the exhaust gas purification system for an internal combustion engine according to the present invention, it is possible to suppress the deterioration of exhaust emission during the execution of regeneration control.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of internal combustion engine and its intake / exhaust system>
Here, the case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment.

  The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 3 and an exhaust passage 2 are connected to the internal combustion engine 1. An air flow meter 7 and a throttle valve 8 are provided in the intake passage 3.

  On the other hand, the exhaust passage 2 is provided with a particulate filter 4 (hereinafter simply referred to as a filter 4) that collects PM in the exhaust. An oxidation catalyst 5 is provided in the exhaust passage 2 upstream of the filter 4. The oxidation catalyst 5 may be a catalyst having an oxidation function, and may be, for example, a NOx catalyst. In this embodiment, the filter 4 constitutes the exhaust gas purification apparatus according to the present invention, and the oxidation catalyst 5 constitutes the catalyst according to the present invention.

  The exhaust passage 2 is provided with a differential pressure sensor 11 that outputs an electrical signal corresponding to the pressure difference in the exhaust passage 2 before and after the filter 3. Further, upstream of the oxidation catalyst 5 and downstream of the oxidation catalyst 5 and upstream of the filter 4 in the exhaust passage 2, an upstream temperature sensor 12 that outputs an electrical signal corresponding to the temperature of the exhaust, and a downstream side. A temperature sensor 13 is provided.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 10 includes an air flow meter 7 and a differential pressure sensor 11, an upstream temperature sensor 12, a downstream temperature sensor 13, a crank position sensor 14 that outputs an electrical signal corresponding to the rotation angle of the crankshaft of the internal combustion engine 1, and An accelerator opening sensor 15 that outputs an electric signal corresponding to the accelerator opening of a vehicle equipped with the internal combustion engine 1 is electrically connected. These output signals are input to the ECU 10.

  The ECU 10 estimates the amount of PM collected in the filter 4 based on the detection value of the differential pressure sensor 11. Further, the ECU 10 calculates the rotation speed of the internal combustion engine 1 based on the detection value of the crank position sensor 14 and calculates the load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 15.

  Further, the ECU 10 is electrically connected to the throttle valve 8 and the fuel injection valve of the internal combustion engine 1. These are controlled by the ECU 10.

<Filter regeneration control>
In the present embodiment, when the amount of collected PM in the filter 4 becomes equal to or greater than the first predetermined collected amount, filter regeneration control is started to oxidize and remove PM. Here, the first predetermined collection amount is an amount smaller than the collection amount that excessively affects the operating state of the internal combustion engine 1, and the filter 4 is overheated when PM is oxidized. The amount is less than the amount collected. This first predetermined collection amount is determined in advance by experiments or the like. In the present embodiment, the PM collection amount in the filter 4 is equal to or greater than the first predetermined collection amount, which corresponds to the predetermined condition according to the present invention.

In the filter regeneration control according to the present embodiment, the exhaust gas raising control for raising the temperature of the engine exhaust gas is executed, and the auxiliary fuel injection is executed in the internal combustion engine 1 at a time after the main fuel injection, whereby the oxidation catalyst 5 is controlled. Fuel is supplied as a reducing agent. Examples of the exhaust gas temperature raising control include control for retarding the main fuel injection timing in the internal combustion engine 1 and control for controlling the throttle valve 8 in the valve closing direction.

  Further, the auxiliary fuel injection is executed at a timing such that at least a part of the fuel injected by the auxiliary fuel injection is discharged from the internal combustion engine 1 in an unburned state. The fuel injection amount (sub fuel injection amount) at the time of executing the sub fuel injection is controlled so that the temperature of the filter 4 becomes a predetermined filter temperature. Here, the predetermined filter temperature is a temperature at which collected PM can be oxidized and removed, and the temperature at which deterioration of the filter 4 can be suppressed. This predetermined filter temperature is determined in advance by experiments or the like. By executing such filter regeneration control, the temperature of the filter 4 rises, and as a result, PM is oxidized and removed.

<Temperature change of filter inflow exhaust>
Here, the relationship between the temperature changes of the engine exhaust exhaust, the central portion of the oxidation catalyst, and the filter inflow exhaust will be described with reference to FIG. The vertical axes of (a), (b), and (c) of FIG. 2 respectively represent the temperature Tex of the engine exhaust exhaust, the temperature Tcc of the central portion of the oxidation catalyst 5 (hereinafter referred to as the catalyst central portion temperature Tcc), the filter It represents the temperature Tfin of the inflowing exhaust. T1, T2, and T3 on these vertical axes represent the same temperature. Also, the horizontal axes of (a), (b), and (c) in FIG. 2 represent time.

  In FIG. 2, ta represents the time when the operating state of the internal combustion engine 1 is in a transient operating state in which the load and the rotational speed are reduced. Further, tc in FIG. 2 represents a time when the filter regeneration control is started when the amount of PM collected in the filter 4 is equal to or greater than the first predetermined amount of collection.

  When the operating state of the internal combustion engine becomes a transient operating state as described above at the time ta in FIG. 2, the temperature Tex of the engine exhaust exhaust begins to decrease. Along with this, the temperature Tfin of the oxidation catalyst 5 and the filter inflow exhaust gas also decreases.

  At this time, since the oxidation catalyst 5 has a heat capacity, the temperature of the oxidation catalyst 5 gradually decreases from the upstream portion along the flow of the exhaust gas. For this reason, the temperature of the downstream portion of the oxidation catalyst 5 starts to fall later than that of the upstream portion and the central portion of the oxidation catalyst 5. Even after the upstream portion and the central portion of the oxidation catalyst 5 are at a relatively low temperature, the downstream portion of the oxidation catalyst 5 passes through the oxidation catalyst 5 if the downstream portion of the oxidation catalyst 5 is at a relatively high temperature. The exhaust gas to be heated is heated. Therefore, as shown in FIG. 2, the temperature drop of the filter inflow exhaust gas is delayed more than the temperature drop of the upstream part and the middle stream part of the oxidation catalyst 5. As a result, the temperature Tfin of the filter inflow exhaust begins to decrease at the time tb in FIG. Here, a period (a period from ta to tb in FIG. 2) from when the temperature Tex of the engine exhaust exhaust begins to decrease until the temperature Tfin of the filter inflow exhaust begins to decrease is defined as a temperature decrease delay time Δtdr.

  As described above, when the operating state of the internal combustion engine 1 becomes a transient operating state and the temperature Tex of the engine exhaust exhaust gas decreases, the temperature Tfin of the filter inflow exhaust gas decreases later than the catalyst central portion temperature Tcc. Therefore, as long as a sufficient time has not elapsed since the temperature Tex of the engine exhaust exhaust gas starts to decrease and the temperature Tfin of the filter inflow exhaust gas is decreasing, as shown in FIG. The temperature of the filter inflowing exhaust gas temperature Tfin may be higher than the temperature at the center.

  On the other hand, when the filter regeneration control is started at the time tc in FIG. 2, that is, while the temperature Tfin of the filter inflow exhaust gas is decreasing, the temperature Tex of the engine exhaust exhaust begins to increase. Along with this, the temperature of the oxidation catalyst 5 rises, and further the temperature Tfin of the filter inflow exhaust gas also rises. At this time, the temperature Tfin of the exhaust gas flowing into the filter rises later than the temperatures of the upstream portion and the central portion of the oxidation catalyst 5 as in the case where the engine exhaust exhaust Tex decreases. As a result, the temperature Tfin of the filter inflow exhaust begins to rise at the time td in FIG. Here, a period (a period from tc to td in FIG. 2) from when the temperature Tex of the engine exhaust gas begins to rise until the temperature Tfin of the filter inflow exhaust begins to fall is defined as a temperature rise delay time Δtur.

<Sub fuel injection amount control>
Next, in the filter regeneration control according to the present embodiment, the control of the sub fuel injection amount when executing the sub fuel injection, that is, the control of the fuel supply amount to the oxidation catalyst 5 will be described. In the present embodiment, the temperature Tfin of the filter inflowing exhaust gas is detected by the downstream temperature sensor 13. When executing the auxiliary fuel injection, a reference auxiliary fuel injection amount that is a reference value for the auxiliary fuel injection amount is determined based on the temperature Tfin of the exhaust gas flowing into the filter and the intake air amount of the internal combustion engine 1.

  However, as described above, after the operation state of the internal combustion engine 1 becomes a transient operation state in which the load and the rotational speed thereof are reduced, and while the temperature Tfin of the filter inflow exhaust gas is decreasing, In some cases, the temperature Tfin of the exhaust gas flowing into the filter is higher than the temperatures of the upstream and central portions of the oxidation catalyst 5. In such a case, the amount of PM collected in the filter 4 is equal to or greater than the first predetermined amount of collection, and the filter regeneration control is executed, so that the auxiliary fuel injection is performed with the reference auxiliary fuel injection amount as the auxiliary fuel injection amount. In this case, the amount of fuel supplied to the oxidation catalyst 5 may be excessive.

  Therefore, in the present embodiment, the amount of change per unit time of the temperature Tfin of the filter inflow exhaust gas when the filter regeneration control is started, that is, when the amount of PM trapped in the filter 4 becomes the first predetermined trapped amount. The exhaust gas temperature change rate α is calculated. When the temperature Tfin of the exhaust gas flowing into the filter is decreasing, the exhaust gas temperature change rate α is a negative value. When the exhaust gas temperature change rate α is a negative value, the reference fuel injection amount is corrected so as to be smaller as the exhaust gas temperature change rate α is smaller (the exhaust gas change rate α is larger), Sub fuel injection is executed with this correction amount as the initial sub fuel injection amount.

  When the temperature Tfin of the filter inflow exhaust gas decreases due to the decrease in the temperature Tex of the engine exhaust exhaust gas, the exhaust gas temperature change rate α increases as time elapses from the time when the temperature Tfin of the filter inflow exhaust gas starts to decrease. (The absolute value of the exhaust gas temperature change rate α is small). Further, the temperature difference between the filter inflow exhaust gas and the upstream portion and the downstream portion of the oxidation catalyst 5 becomes smaller as time elapses from the time when the temperature Tfin of the filter inflow exhaust gas starts to decrease.

  Therefore, according to the control as described above, when the temperature Tfin of the filter inflow exhaust gas is higher than the temperatures of the upstream and central portions of the oxidation catalyst 5 at the start of execution of the filter regeneration control, the larger the temperature difference is, That is, the lower the temperature of the upstream and central portions of the oxidation catalyst 5, the smaller the amount of sub fuel injection in the filter regeneration control. Thereby, it is possible to suppress the amount of fuel supplied to the oxidation catalyst 5 from being excessive with respect to the temperature of the oxidation catalyst 5.

Note that after the start of the filter regeneration control, the temperature Tfin of the filter inflow exhaust gas and the temperature of the oxidation catalyst 5 are substantially equal when the temperature of the filter inflow exhaust gas temperature Tfin begins to rise. Therefore, in this embodiment, after the start of the filter regeneration control, while the exhaust gas temperature change rate α is a negative value, the initial auxiliary fuel injection amount is set as the auxiliary fuel injection amount, and the exhaust gas temperature change rate α becomes zero. After the time point, the reference auxiliary fuel injection amount is set as the auxiliary fuel injection amount.

<Control routine for filter regeneration control>
Next, a control routine for filter regeneration control according to the present embodiment will be described with reference to the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, first, in S101, the ECU 10 determines whether or not the PM collection amount Qpm in the filter 4 is equal to or greater than the first predetermined collection amount Q1. When an affirmative determination is made in S101, the ECU 10 proceeds to S102, and when a negative determination is made, the ECU 10 once ends the execution of this routine.

  In S102, the ECU 10 performs the exhaust gas temperature raising control described above.

  Next, the ECU 10 determines whether or not the engine exhaust exhaust Tex detected by the upstream temperature sensor 12 is equal to or higher than the activation temperature Ta of the oxidation catalyst 5. If an affirmative determination is made in S103, the ECU 10 proceeds to S104. If a negative determination is made, the ECU 10 repeats S103.

  The ECU 10 having proceeded to S104 determines whether or not the exhaust gas temperature change rate α at the start of execution of the filter regeneration control, that is, at the start of the exhaust gas temperature increase control is a negative value. Here, the exhaust gas temperature change rate α may be calculated by subtracting the temperature of the filter inflow exhaust one second before the start of the exhaust gas temperature increase control from the temperature of the filter inflow exhaust gas at the start of the exhaust gas temperature increase control. If an affirmative determination is made in S104, the ECU 10 proceeds to S109, and if a negative determination is made, the ECU 10 proceeds to S105.

  The ECU 10 having proceeded to S105 calculates a reference auxiliary fuel injection amount Qfbase based on the current intake air amount of the internal combustion engine 1 and the temperature Tfin of the filter inflow exhaust gas.

  Next, the ECU 10 proceeds to S106, and executes the auxiliary fuel injection using the reference auxiliary fuel injection amount Qfbase as the auxiliary fuel injection amount. Thereby, the temperature of the filter 5 is raised to the target filter temperature.

  Next, the ECU 10 proceeds to S107 and determines whether or not the PM collection amount Qpm in the filter 5 is equal to or less than the second predetermined collection amount Q2. Here, the second predetermined collection amount Q2 is a threshold amount that can be determined that it takes some time before the PM collection amount becomes the first predetermined collection amount Q1 again, that is, the PM collection amount is This is a threshold value that can be judged to be sufficiently reduced. The second predetermined collection amount Q2 is also a predetermined amount by experiment or the like. If an affirmative determination is made in S107, the ECU 10 proceeds to S108, and if a negative determination is made, the ECU 10 returns to S105.

  In S108, the ECU 10 stops the exhaust gas temperature raising control and the auxiliary fuel injection. That is, the execution of the filter regeneration control is stopped. Thereafter, the ECU 10 temporarily stops the execution of this routine.

  On the other hand, the ECU 10 that has proceeded to S109 calculates the reference auxiliary fuel injection amount Qfbase based on the current intake air amount of the internal combustion engine 1 and the temperature Tfin of the filter inflow exhaust gas, as in S105.

  Next, the ECU 10 proceeds to S110 and derives an initial correction coefficient c for correcting the reference auxiliary fuel injection amount Qfbase based on the exhaust gas temperature change rate α. Here, the initial correction coefficient c is derived from a map representing the relationship between the exhaust gas temperature change rate α and the initial correction coefficient c as shown in FIG. In this map, the exhaust gas temperature change rate α is a negative value, and the correction coefficient is a positive value and a value smaller than 1. In this map, the initial correction coefficient c decreases as the exhaust gas temperature change rate α decreases.

  Next, the ECU 10 proceeds to S111, and calculates the initial sub fuel injection amount Qfe by multiplying the reference sub fuel injection amount Qfbase by the initial correction coefficient c.

  Next, the ECU 10 proceeds to S112 and executes the auxiliary fuel injection with the initial auxiliary fuel injection amount Qfe as the auxiliary fuel injection amount.

  Next, the ECU 10 proceeds to S113, and determines whether or not the exhaust gas temperature change rate α ′ at the current time is 0 or more. That is, it is determined whether or not the temperature Tfin of the filter inflow exhaust gas has started to rise. If an affirmative determination is made in S113, the ECU 10 proceeds to S105. Thus, after the start of the execution of the auxiliary fuel injection, the auxiliary fuel injection is executed with the reference auxiliary fuel injection amount Qfbase as the auxiliary fuel injection amount after the time when the temperature Tfin of the exhaust gas flowing into the filter and the temperature of the oxidation catalyst 5 become substantially equal. Is done. On the other hand, if a negative determination is made in S113, the ECU 10 returns to S109.

  According to the control routine described above, when the temperature Tfin of the filter inflow exhaust gas is decreasing at the start of execution of the filter regeneration control, that is, the temperature Tfin of the filter inflow exhaust gas is increased in the upstream portion of the oxidation catalyst 5 and When the temperature is higher than the central portion, the sub fuel injection amount in the filter regeneration control becomes smaller as the temperatures of the upstream portion and the central portion of the oxidation catalyst 5 are lower. Thereby, it is possible to suppress the amount of fuel supplied to the oxidation catalyst 5 from being excessive with respect to the temperature of the oxidation catalyst 5.

  Therefore, according to the present embodiment, it is possible to suppress the deterioration of exhaust emission when the filter regeneration control is executed. Moreover, deterioration of fuel consumption can also be suppressed.

<Modification>
Next, as a modification of the present embodiment, a case where a NOx catalyst is provided instead of the filter 4 will be described. In such a case, SOx poisoning regeneration control is performed to reduce SOx stored in the NOx catalyst. In this case, the NOx catalyst constitutes the exhaust purification device according to the present invention. The SOx regeneration control corresponds to the regeneration control according to the present invention.

  In the SOx poisoning regeneration control, as in the filter regeneration control, fuel is supplied to the oxidation catalyst 5 by sub fuel injection so as to raise the temperature of the NOx catalyst. As a result, the temperature of the NOx catalyst is raised, and fuel is supplied as a reducing agent to the NOx catalyst by sub fuel injection, so that the environment around the NOx catalyst becomes a reducing atmosphere, and SOx is reduced.

  In such a configuration, the temperature change of the exhaust gas flowing into the NOx catalyst is the same as the temperature change of the filter inflow exhaust gas described above. Therefore, the sub fuel injection amount in the SOx poisoning regeneration control is controlled in the same manner as in the filter regeneration control. As a result, it is possible to suppress the deterioration of exhaust emission during execution of the SOx poisoning regeneration control. Moreover, deterioration of fuel consumption can also be suppressed.

Since the schematic configuration of the internal combustion engine and the intake / exhaust system thereof according to the present embodiment is the same as that of the first embodiment, description thereof is omitted. Also in the present embodiment, the filter regeneration control is performed by executing the exhaust gas temperature raising control and the auxiliary fuel injection as in the first embodiment.

<Sub fuel injection amount control>
Here, in the filter regeneration control according to the present embodiment, the control of the sub fuel injection amount when executing the sub fuel injection will be described.

  As described above, when the operating state of the internal combustion engine 1 becomes a transient operating state in which the load and the rotational speed thereof decrease, the temperature Tex of the engine exhaust exhaust gas decreases, and then the temperature Tex of the engine exhaust exhaust gas begins to decrease. The temperature Tfin of the filter inflow exhaust begins to decrease after the temperature decrease delay time Δtdr has elapsed. The temperature decrease delay time Δtdr becomes longer as the amount of heat of the oxidation catalyst 5 at the time when the operation state of the internal combustion engine 1 becomes the transient operation state as described above, and the operation state of the internal combustion engine 1 becomes as described above. The shorter the amount of intake air at the time of transient operation, the shorter.

  Further, after the operating state of the internal combustion engine 1 becomes the transient operation state as described above, the filter regeneration control is executed while the temperature Tfin of the filter inflow exhaust gas is decreasing, whereby the engine exhaust exhaust gas temperature Tex. Rises, the temperature Tfin of the filter inflow exhaust begins to rise after the temperature rise delay time Δtur has elapsed since the temperature Tex of the engine exhaust exhaust begins to rise.

  The temperature increase delay time Δtur at this time is substantially the same as the temperature decrease delay time Δtdr when the operation state of the internal combustion engine 1 becomes a transient operation state.

  On the other hand, when the execution of the filter regeneration control is started, the temperature of the upstream portion and the central portion of the oxidation catalyst 5 starts to rise relatively quickly as the engine exhaust gas is heated. Therefore, when the filter regeneration control is executed and the sub fuel injection is performed while the temperature Tfin of the exhaust gas flowing into the filter is decreasing, the sub fuel injection amount is calculated by the same method as in the first embodiment. The execution of the auxiliary fuel injection may be started as the amount Qfe, and the auxiliary fuel injection amount may be gradually increased after the auxiliary fuel injection is started.

  Further, at the time when the temperature Tfin of the filter inflow exhaust begins to increase after the start of the filter regeneration control, the filter inflow exhaust and the upstream and central portions of the oxidation catalyst 5 have substantially the same temperature. Therefore, when the temperature Tfin of the filter inflow exhaust gas starts to rise, the fuel supply to the oxidation catalyst 5 is achieved even if the sub fuel injection amount is increased to the reference sub fuel injection amount Qfbase calculated by the same method as in the first embodiment. It is unlikely that the amount will be excessive. Therefore, as the temperature rise delay time Δtur of the exhaust gas flowing into the filter is shorter, the sub fuel injection amount can be increased more quickly from the initial sub fuel injection amount Qfe to the reference sub fuel injection amount Qfbase. The shorter the temperature drop delay time Δtdr, the shorter the temperature rise delay time Δtur.

  Therefore, in this embodiment, when the filter regeneration control is started and the auxiliary fuel injection is performed while the temperature Tfin of the filter inflow exhaust gas is decreasing, the auxiliary fuel injection is performed using the initial auxiliary fuel injection amount Qfe as the auxiliary fuel injection amount. And the sub fuel injection amount is gradually increased. The speed of increase at this time is increased as the temperature drop delay time Δtdr when the operating state of the internal combustion engine 1 becomes a transient operating state is shorter.

By such control, the time until the temperature Tfin of the filter inflow exhaust starts to increase after the start of the filter regeneration control, that is, the temperature at which the filter inflow exhaust and the upstream and central portions of the oxidation catalyst 5 are substantially the same. The shorter the time to become, the faster the amount of fuel supplied to the oxidation catalyst 5 is increased. Therefore, in the filter regeneration control, more fuel can be supplied to the oxidation catalyst 5 while suppressing an excessive amount of fuel supply to the oxidation catalyst 5. Therefore, according to this embodiment, it is possible to raise the temperature of the filter 4 more quickly while suppressing deterioration of exhaust emission.

<Control routine for filter regeneration control>
Next, the control routine of the filter regeneration control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is executed at predetermined intervals during the operation of the internal combustion engine 1. Since S102 to S103 and S105 to S108 in this routine are the same as the control routine for the filter regeneration control according to the first embodiment, the same steps are denoted by the same reference numerals and the description thereof is omitted.

  In this routine, first, in S201, the ECU 10 determines whether or not the operating state of the internal combustion engine 1 has shifted to a transient operating state in which the load and the rotational speed are reduced. If an affirmative determination is made in S201, the ECU 10 proceeds to S202, and if a negative determination is made, the ECU 10 ends the execution of this routine.

  The ECU 10 having proceeded to S202 determines whether or not the exhaust gas temperature change rate α ″ at the present time has become a negative value, that is, whether or not the temperature Tfin of the filter inflow exhaust gas has started to decrease. If an affirmative determination is made in S202, the ECU 10 proceeds to S203, and if a negative determination is made, the ECU 10 once ends the execution of this routine.

  The ECU 10 that has proceeded to S203 calculates the temperature decrease delay time Δtdr, and then proceeds to S101.

  Further, in this routine, it can be determined that the exhaust gas temperature change rate α at the time when the exhaust gas temperature raising control is started in S102 is a negative value. Therefore, if an affirmative determination is made in S103, the ECU 10 proceeds to S109, and calculates the reference auxiliary fuel injection amount Qfbase by the same method as in the first embodiment.

  In S112, the ECU 10 executes the auxiliary fuel injection using the initial auxiliary fuel injection amount Qfe calculated by the same method as in the first embodiment as the auxiliary fuel injection amount, and then proceeds to S213.

  In step S213, the ECU 10 calculates a reference auxiliary fuel injection amount Qfbase based on the current intake air amount of the internal combustion engine 1 and the temperature Tfin of the filter inflow exhaust gas.

  Next, the ECU 10 proceeds to S214, and calculates an elapsed time ts from the start of the exhaust gas temperature raising control to the current time (hereinafter simply referred to as an elapsed time ts).

  Next, the ECU 10 proceeds to S215, and derives an increase correction coefficient c ′ for determining the next sub fuel injection amount based on the initial correction coefficient c, the temperature decrease delay time Δtdr, and the elapsed time ts.

  Here, a method for deriving the increase correction coefficient c ′ will be described. As described above, the temperature rise delay time Δtur, which is the time from when the filter regeneration control is started until the temperature Tfin of the filter inflow exhaust begins to rise, is substantially the same as the temperature drop delay time Δtdr. From this, it is determined that the temperature Tfin of the filter inflow exhaust gas and the temperature of the oxidation catalyst 5 are substantially equal after the time when the elapsed time from the start of the filter regeneration control becomes the same time as the temperature decrease delay time Δtdr. I can do it. That is, at this time, the sub fuel injection amount can be increased to the reference sub fuel injection amount Qfbase.

Therefore, in this embodiment, a map as shown in FIG. 6 is created to derive the increase correction coefficient c ′. In this map, the vertical axis represents the increase correction coefficient c ′, and the horizontal axis represents the elapsed time ts. The increase correction coefficient c ′ when the elapsed time ts is 0 is set as the initial correction coefficient c. Further, the increase correction coefficient c ′ when the elapsed time ts is the temperature decrease delay time Δtdr is set to 1. Further, a straight line representing the relationship between the elapsed time ts and the increase correction coefficient c ′ is created by connecting these two points.

  According to the map created in this way, the increase correction coefficient c ′ increases with time. Further, as the temperature decrease delay time Δtdr is shorter, the slope of the straight line shown in FIG. 6 becomes larger, so that the increase correction coefficient c ′ becomes a larger value more quickly.

  Next, the ECU 10 proceeds to S216, and calculates the intermediate sub fuel injection amount Qfn, which is the sub fuel injection amount at the present time, by multiplying the reference sub fuel injection amount Qfbase by the increase correction coefficient c ′.

  Next, the ECU 10 proceeds to S217 and executes the auxiliary fuel injection using the intermediate auxiliary fuel injection amount Qfn as the auxiliary fuel injection amount.

  Next, the ECU 10 proceeds to S113, and determines whether or not the current exhaust gas change rate α ′ has become 0 or more, that is, whether or not the temperature Tfin of the filter inflowing exhaust gas has started to rise. If an affirmative determination is made in S113, the ECU 10 proceeds to S105. On the other hand, if a negative determination is made in S113, the ECU 10 returns to S213.

  According to the control routine described above, when the auxiliary fuel injection is performed while the temperature Tfin of the filter inflow exhaust gas is decreasing, as in the first embodiment, the initial auxiliary fuel injection amount Qfe is used as the auxiliary fuel injection amount. Execution of fuel injection is started. Further, after the execution of the sub fuel injection is started using the initial sub fuel injection amount Qfe as the sub fuel injection amount, the sub fuel injection amount is gradually increased as time passes. The increasing speed at this time becomes faster as the temperature drop delay time Δtdr when the operating state of the internal combustion engine 1 becomes a transient operating state is shorter.

  In this embodiment as well, when a NOx catalyst is provided instead of the filter 4, the control of the sub fuel injection amount during the filter regeneration control according to this embodiment is performed during the SOx poisoning regeneration control as in the first embodiment. You may apply to control of the amount of sub fuel injection. As a result, it is possible to raise the temperature of the NOx catalyst more quickly while suppressing deterioration of exhaust emission.

  In the first and second embodiments, the case where fuel is supplied to the oxidation catalyst 5 by executing sub fuel injection in the internal combustion engine 1 has been described. However, a fuel addition valve is provided in the exhaust passage 2 upstream of the oxidation catalyst 5, The fuel may be supplied to the oxidation catalyst 5 by adding fuel from the fuel addition valve.

The figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake / exhaust system. The figure which shows the relationship of the temperature change of engine exhaust_gas | exhaustion, the center part of an oxidation catalyst, and each filter inflow exhaust_gas | exhaustion. 5 is a flowchart illustrating a control routine for filter regeneration control according to the first embodiment. A map showing the relationship between the exhaust gas temperature change rate and the initial correction coefficient. 9 is a flowchart illustrating a control routine for filter regeneration control according to the second embodiment. A map showing the relationship between the elapsed time and the increase correction coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 4 ... Particulate filter 5 ... Oxidation catalyst 7 ... Air flow meter 10 ... ECU
11. ・ Differential pressure sensor 12 ・ ・ Upstream temperature sensor 13 ・ ・ Downstream temperature sensor 14 ・ ・ Crank position sensor 15 ・ ・ Accelerator opening sensor

Claims (2)

An exhaust purification device provided in the exhaust passage of the internal combustion engine;
A catalyst having an oxidation function provided in the exhaust passage upstream of the exhaust purification device;
Inflow exhaust gas temperature detection means for detecting the temperature of inflow exhaust gas that is exhaust gas flowing into the exhaust gas purification device;
An exhaust gas temperature change rate calculating means for calculating an exhaust gas temperature change rate that is a change amount per unit time of the temperature of the inflowing exhaust gas;
Regeneration control execution means for performing regeneration control for increasing the temperature of the exhaust purification device by supplying a reducing agent from the upstream side to the catalyst, thereby regenerating the exhaust purification capability of the exhaust purification device;
A reducing agent supply amount determining means for determining a reducing agent supply amount to the catalyst in the regeneration control,
The regeneration control execution means starts the regeneration control when a predetermined condition is satisfied,
The reducing agent supply amount determining means calculates a reference supply amount that is a reference value of the reducing agent supply amount to the catalyst in the regeneration control based on the intake air amount of the internal combustion engine and the temperature of the inflowing exhaust gas. And when the exhaust temperature change rate when the predetermined condition is satisfied is a negative value, the exhaust temperature change rate is compared when the exhaust temperature change rate is relatively small. The reference supply amount is corrected so as to be smaller than when it is large, and the correction amount is set as an initial supply amount that is a reducing agent supply amount to the catalyst at the initial stage of execution of the regeneration control. An exhaust gas purification system for an internal combustion engine. When the operation state of the internal combustion engine becomes a transient operation state in which the load and the rotational speed thereof are reduced, the time point when the temperature of the inflowing exhaust gas starts to decrease from the time point when the temperature of the exhaust gas discharged from the internal combustion engine starts to decrease Further comprising a temperature decrease delay time calculating means for calculating a temperature decrease delay time that is a period until
When the predetermined condition is satisfied after the operation state of the internal combustion engine becomes the transient operation state, and when the exhaust temperature change rate at the time when the predetermined condition is satisfied is a negative value, The supply amount determining means sets the reducing agent supply amount at the start of reducing agent supply to the catalyst in the regeneration control as the initial supply amount, and gradually increases the reducing agent supply amount after starting the reducing agent supply, 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein an increasing speed when increasing the supply amount of the reducing agent is increased as the temperature decrease delay time is shorter.

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