JP2020193600A - Exhaust emission control device and control method for internal combustion engine - Google Patents

Abstract

To suppress an increase in a concentration of HC in exhaust gas discharged from an NOx catalyst during execution of regeneration control.SOLUTION: An exhaust emission control device for an internal combustion engine 1 includes: an oxidation catalyst 22 and a selective reduction type NOx catalyst 24 which are provided in an exhaust passage 4 from the upstream side in this order; and a control unit 100 configured to execute regeneration control for increasing a temperature of exhaust gas. When the regeneration control is not executed, the control unit estimates adsorbed HC amount of the NOx catalyst. When the regeneration control is executed, the control unit executes high-speed temperature increase control for increasing a temperature of the NOx catalyst at high speed after performing low-speed temperature increase control for increasing the temperature of the NOx catalyst at low speed, and changes switching timing for switching from the low-speed temperature increase control to the high-speed temperature increase control in accordance with the estimated adsorbed HC amount.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust gas purification device and a control method for an internal combustion engine.

In an exhaust gas purification device for an internal combustion engine, particularly a diesel engine, one in which an oxidation catalyst, a filter and a selective reduction NOx catalyst are provided in order from the upstream side in an exhaust passage is known. It is also known to perform regeneration control for raising the temperature of the exhaust gas in order to recover the performance of the filter by burning and removing the particulate matter collected in the filter. In the regeneration control, the HC concentration of the exhaust gas is increased by post-injection or the like, and the exhaust gas temperature is raised by burning this HC with an oxidation catalyst.

Japanese Unexamined Patent Publication No. 2011-256847

By the way, the NOx catalyst has an HC adsorption ability. If regeneration control is executed while a large amount of HC is adsorbed on the NOx catalyst and a relatively high temperature exhaust gas is supplied to the NOx catalyst, the HC adsorbed on the NOx catalyst is desorbed and the NOx catalyst is desorbed. It may be released at once to the downstream side of. In this case, the exhaust gas having a high HC concentration is discharged to the atmosphere, which is not only environmentally unfavorable, but also may generate white smoke and an offensive odor.

Therefore, the present disclosure was devised in view of such circumstances, and an object of the present invention is to provide an exhaust gas purification device and a control method for an internal combustion engine capable of suppressing an increase in the HC concentration of exhaust gas discharged from a NOx catalyst during execution of regeneration control. To do.

According to one aspect of the present disclosure
Oxidation catalyst and selective reduction NOx catalyst provided in order from the upstream side in the exhaust passage of the internal combustion engine,
A control unit configured to perform regeneration control to raise the temperature of the exhaust,
With
The control unit
The amount of adsorbed HC of the NOx catalyst is estimated when the regeneration control is not executed.
When the regeneration control is executed, after performing the low-speed temperature rise control for raising the temperature of the exhaust gas at a low speed, the high-speed temperature rise control for raising the temperature of the exhaust gas at a high speed is performed, and the low-speed temperature rise control is performed according to the estimated adsorption HC amount. An exhaust gas purification device for an internal combustion engine is provided, which is characterized by changing the switching timing for switching from to high-speed temperature rise control.

Preferably, the control unit delays the switching timing as the estimated amount of adsorption HC increases.

Preferably, when the estimated adsorption HC amount is equal to or greater than a predetermined threshold value, the control unit changes the switching timing according to the estimated adsorption HC amount.

Preferably, the control unit is
Low-speed temperature rise control is performed until the inlet temperature of the NOx catalyst rises from a predetermined first temperature to a second temperature, and when the inlet temperature of the NOx catalyst reaches the second temperature, low-speed temperature rise control is performed. Switch to high-speed temperature rise control,
The larger the estimated amount of adsorbed HC, the longer the execution time of the low-speed temperature rise control.

Preferably, the control unit stores in advance a map that defines the relationship between the adsorbed HC amount and the execution time of the low-speed temperature rise control, and executes the low-speed temperature rise control corresponding to the adsorption HC amount estimated from the map. Calculate the time.

Preferably, the control unit sets the hourly target temperature of the NOx catalyst inlet temperature during the low-speed temperature rise control based on the execution time of the low-speed temperature rise control, and actually operates the NOx catalyst during the low-speed temperature rise control. The amount of fuel supplied to the oxidation catalyst is feedback-controlled so that the inlet temperature of the oxide catalyst approaches the target temperature.

Preferably, the control unit causes the in-cylinder injector to perform after-injection during low-speed temperature rise control, and additionally causes the in-cylinder injector to perform post-injection in addition to the after-injection during high-speed temperature rise control. Alternatively, let the exhaust pipe injector execute the exhaust pipe injection.

Preferably, the exhaust purification device further comprises another oxidation catalyst provided in the exhaust passage downstream of the NOx catalyst.
The control unit sets the switching timing from the low-speed temperature rise control to the high-speed temperature rise control so that the HC concentration of the exhaust gas discharged from the other oxidation catalyst does not exceed a predetermined upper limit value when the regeneration control is executed. ..

According to other aspects of the disclosure,
It is a control method of an internal combustion engine provided with an oxidation catalyst and a selective reduction NOx catalyst provided in order from the upstream side in the exhaust passage.
The first step of estimating the amount of adsorbed HC of the NOx catalyst when the regeneration control for raising the temperature of the exhaust gas is not executed, and
When the regeneration control is executed, the low-speed temperature rise control for raising the temperature of the exhaust at a low speed is performed, and then the high-speed temperature rise control for raising the temperature of the exhaust at a high speed is performed, and the low-speed temperature rise control is performed according to the estimated adsorption HC amount. The second step of changing the switching timing to switch from to high-speed temperature rise control,
A method for controlling an internal combustion engine is provided.

According to the present disclosure, it is possible to suppress an increase in the HC concentration of the exhaust gas discharged from the NOx catalyst when the regeneration control is executed.

It is a schematic diagram which shows the structure of the Embodiment of this disclosure. It is a time chart which shows the fuel injection method at the time of each control. It is a figure which shows each map and the like. It is a time chart which shows the change of each value at the time of a reproduction control. It is a flowchart which shows the control procedure of this embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

FIG. 1 is a schematic view showing the configuration of the present embodiment. The internal combustion engine (also referred to as an engine) 1 is a multi-cylinder engine mounted on a vehicle (not shown). In the present embodiment, the vehicle is a large vehicle such as a truck, and the engine 1 as a vehicle power source mounted on the large vehicle is an in-line 4-cylinder diesel engine. However, the type, type, use, and the like of the vehicle and the internal combustion engine are not particularly limited. For example, the vehicle may be a small vehicle such as a passenger car, and the engine 1 may be a gasoline engine.

The engine may be mounted on a moving body other than a vehicle, for example, a ship, a construction machine, or an industrial machine. Further, the engine does not have to be mounted on a moving body, and may be a stationary engine.

The engine 1 includes an engine main body 2, an intake passage 3 and an exhaust passage 4 connected to the engine main body 2, a turbocharger 14, and a fuel injection device 5. The engine body 2 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and movable parts such as a piston, a crankshaft, and a valve housed therein.

The fuel injection device 5 includes a common rail type fuel injection device, and includes a fuel injection injector 7 provided in each cylinder and a common rail 8 connected to the injector 7. The injector 7 is an in-cylinder injector for supplying fuel into the cylinder of the corresponding cylinder, and in the case of the present embodiment, the fuel is directly injected into the cylinder. The common rail 8 stores the fuel injected from the injector 7 in a high pressure state.

The intake passage 3 is mainly defined by an intake manifold 10 connected to the engine body 2 (particularly a cylinder head) and an intake pipe 11 connected to the upstream end of the intake manifold 10. The intake manifold 10 distributes and supplies the intake air sent from the intake pipe 11 to the intake ports of each cylinder. The intake pipe 11 is provided with an air cleaner 12, an air flow meter 13, a turbocharger 14 compressor 14C, an intercooler 15, and an electronically controlled intake throttle valve 16 in this order from the upstream side. The air flow meter 13 is a sensor for detecting the intake air amount per unit time of the engine 1, that is, the intake flow rate, and is also called a mass air flow (MAF) sensor or the like.

The exhaust passage 4 is mainly defined by an exhaust manifold 20 connected to the engine body 2 (particularly a cylinder head) and an exhaust pipe 21 connected to the downstream side of the exhaust manifold 20. The exhaust manifold 20 collects the exhaust gas sent from the exhaust port of each cylinder. A turbine 14T of a turbocharger 14 is provided between the exhaust pipe 21 or the exhaust manifold 20 and the exhaust pipe 21.

An oxidation catalyst 22, a filter 23, and a selective reduction NOx catalyst 24 are provided in the exhaust passage 4 on the downstream side of the turbine 14T in this order from the upstream side. Further, an ammonia oxidation catalyst 26, which is another oxidation catalyst, is provided in the exhaust passage 4 on the downstream side of the NOx catalyst 24. An addition valve 25 for adding urea water as a reducing agent is provided in the exhaust passage 4 between the filter 23 and the NOx catalyst 24.

The oxidation catalyst 22 oxidizes and purifies the unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas, heats and raises the exhaust gas with the heat of reaction at this time, and NO ₂ in the exhaust gas. Oxidizes to. The filter 23 is composed of a so-called continuously regenerating type filter with a catalyst, and collects particulate matter (PM (Particulate Matter)) contained in the exhaust gas and burns the collected PM by catalytic action. The filter 23 can be regarded as a kind of catalyst. The NOx catalyst 24 reacts ammonia derived from urea water added from the addition valve 25 with NOx to reduce and purify NOx in the exhaust gas. The ammonia oxidation catalyst 26 oxidizes and purifies excess ammonia discharged from the NOx catalyst 24.

An exhaust pipe injector 38 is provided in the exhaust passage 4 on the upstream side of the oxidation catalyst 22. The exhaust pipe injector 38 can inject fuel into the exhaust passage 4 or the exhaust pipe 21 during regeneration control described later. Hereinafter, such fuel injection into the exhaust passage 4 will be referred to as exhaust pipe injection. In the present embodiment, the exhaust pipe injector 38 is provided on the downstream side of the turbine 14T, but the installation position thereof can be changed.

The engine 1 also includes an exhaust gas recirculation (EGR) device 30. The EGR device 30 includes an EGR passage 31 for recirculating a part (referred to as EGR gas) of the exhaust gas in the exhaust passage 4 (particularly in the exhaust manifold 20) into the intake passage 3 (particularly in the intake manifold 10), and an EGR. An EGR cooler 32 for cooling the EGR gas flowing through the passage 31 and an EGR valve 33 for adjusting the flow rate of the EGR gas are provided.

The vehicle is equipped with a control device for controlling the engine 1. The control device includes a control unit, a circuit element (circuitry), or an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 that forms a controller. The ECU 100 includes a CPU (Central Processing Unit) having a calculation function, ROM (Read Only Memory) and RAM (Random Access Memory) as storage media, an input / output port, and a storage device other than ROM and RAM. The ECU 100 is configured and programmed to control an in-cylinder injector 7, an intake throttle valve 16, an addition valve 25, an EGR valve 33, and an exhaust pipe injector 38.

The control device includes the following sensors in addition to the above-mentioned air flow meter 13. That is, a rotation speed sensor 40 for detecting the rotation speed of the engine, specifically, a rotation speed (rpm) per minute, and an accelerator opening degree sensor 41 for detecting the accelerator opening degree are provided. Further, exhaust temperature sensors 42, 43, and 44 for detecting the exhaust temperature (referred to as the inlet temperature) at the inlets of the oxidation catalyst 22, the filter 23, and the NOx catalyst 24 are provided. Further, a differential pressure sensor 45 for detecting the differential pressure of the exhaust pressure at the inlet and outlet of the filter 23 is provided. The output signals of these sensors are sent to the ECU 100 via a signal transmission wire or wireless communication (not shown).

Next, the control of this embodiment will be described.

First, the regeneration control (exhaust gas temperature rise control) for raising the temperature of the exhaust gas will be described. When the differential pressure detected by the differential pressure sensor 45 reaches a predetermined upper limit threshold value or more, the ECU 100 considers that the PM collection amount of the filter 23 has reached the vicinity of fullness, and burns and removes the collected PM. , Playback control is performed. At this time, the ECU 100 causes the in-cylinder injector 7 to perform after-injection and post-injection, which will be described later, and burns the additional fuel produced by these with the oxidation catalyst 22 to raise the temperature of the exhaust gas supplied to the filter 23. As a result, PM combustion is promoted in the filter 23, and PM in the filter 23 is removed. Then, the PM collecting ability of the filter 23 is restored, and the filter 23 is regenerated.

In addition, instead of the post injection, the exhaust pipe injection by the exhaust pipe injector 38 may be performed. Further, the start condition of the regeneration control may be that the amount of adsorbed HC of the NOx catalyst 24 reaches a predetermined upper limit threshold value or more, which will be described in detail later.

By the way, the NOx catalyst 24 has an HC adsorption ability of adsorbing HC at a low temperature and desorbing the adsorbed NOx at a high temperature. If the regeneration control is executed with a large amount of HC adsorbed on the NOx catalyst 24 and a relatively high temperature exhaust gas is supplied to the NOx catalyst 24, the HC adsorbed on the NOx catalyst 24 is desorbed. , NOx catalyst 24 may be released at once to the downstream side. In this case, the exhaust gas having a high HC concentration is discharged to the atmosphere, which is not only environmentally unfavorable, but also may generate white smoke and an offensive odor. Hereinafter, this issue will be described in more detail.

The HC adsorption ability exists not only in the NOx catalyst 24 but also in the oxidation catalyst 22 and the filter 23. When the low rotation speed and low load operation of the engine are continued, HC is adsorbed on the oxidation catalyst 22 because the temperature and activity of the oxidation catalyst 22 are low. The HC that could not be treated by the oxidation catalyst 22 is adsorbed on the filter 23 and the NOx catalyst 24. This tendency becomes stronger when the oxidation catalyst 22 has deteriorated over time. When HC is adsorbed on the oxidation catalyst 22, the surface of the oxidation catalyst 22 becomes a gum-like sticky substance, and PM also adheres to the surface of the oxidation catalyst 22, so that the oxidation catalyst 22 tends to be clogged and the processing capacity of the oxidation catalyst 22 is significantly reduced. ..

When the regeneration control is started under such a situation, the temperature of the oxidation catalyst 22 rises, but the rate of temperature rise is slow. Then, in the oxidation catalyst 22, the adsorbed HC is desorbed and discharged to the downstream side, and the HC derived from the additional fuel slips and is discharged to the downstream side without being completely processed.

The HC discharged to the downstream side is adsorbed on the filter 23. Since the temperature rise of the filter 23 is delayed by the heat capacity of the oxidation catalyst 22, HC desorption from the filter 23 is slow. The HC desorbed from the filter 23 is supplied to the NOx catalyst 24 on the downstream side and adsorbed on the NOx catalyst 24. The temperature rise of the NOx catalyst 24 is delayed by the heat capacity of the filter 23. In this way, the temperature is raised one after another from the catalyst on the upstream side, and the adsorbed HC is discharged one after another from the catalyst on the upstream side. The NOx catalyst 24 finally functions like a dam that blocks NOx.

Since the heat capacity of the NOx catalyst 24 is relatively large, there is a relatively large time lag between the temperature rise of the filter 23 and the temperature rise of the NOx catalyst 24. Further, since the HC adsorption capacity of the NOx catalyst 24 is also relatively large, a relatively large amount of HC is adsorbed on the NOx catalyst 24.

The zeolite used as the carrier of the NOx catalyst 24 has an ability to desorb adsorbed HC at a relatively high temperature (for example, 200 ° C. or higher). When a certain amount of time elapses from the start of regeneration control and the NOx catalyst 24 reaches such an HC desorption temperature, the HC adsorbed up to that point may be desorbed from the NOx catalyst 24 at once and released to the downstream side.

Then, the HC concentration of the exhaust gas discharged from the NOx catalyst 24 becomes too high to be processed by the ammonia oxidation catalyst 26, and the exhaust gas having an unacceptably high HC concentration may be released from the ammonia oxidation catalyst 26 to the atmosphere. .. This is of course environmentally unfavorable. In addition, exhaust with a high HC concentration appears as white smoke for a relatively long time and also generates an offensive odor. The ammonia oxidation catalyst 26 can be omitted, but this makes the situation worse.

Therefore, in the present embodiment, in order to solve such a problem, the control described below is carried out by the ECU 100.

Generally, in the present embodiment, the amount of adsorbed HC of the NOx catalyst 24 is estimated when the regeneration control is not executed, that is, when the normal control is executed. Then, when the regeneration control is executed, the NOx catalyst 24 is heated at a low speed, and then the NOx catalyst 24 is heated at a high speed, and then the NOx catalyst 24 is heated at a high speed. , Change the switching timing to switch from low-speed temperature rise control to high-speed temperature rise control.

When the low-speed temperature rise control is performed, the HC desorption rate from the NOx catalyst 24 can be slowed down, and the HC concentration of the exhaust gas discharged from the NOx catalyst 24 can be suppressed to a low level. On the other hand, when the high-speed temperature rise control is performed, the HC concentration of the exhaust gas discharged from the NOx catalyst 24 tends to increase, but the HC desorption rate from the NOx catalyst 24 can be increased.

In the present embodiment, low-speed temperature rise control is performed at the initial stage of regeneration control to desorb the adsorbed HC of the NOx catalyst 24 and reduce the adsorbed amount while suppressing the HC concentration of the exhaust gas from the NOx catalyst 24. Then, when the amount of HC adsorbed by the NOx catalyst 24 decreases to some extent, the temperature rise control is switched to, and the adsorbed HC of the NOx catalyst 24 is more positively desorbed. At this stage, since the amount of HC adsorbed is already low, the HC concentration of the exhaust gas from the NOx catalyst 24 can be kept low even if the desorption rate of the adsorbed HC is increased.

In particular, the switching timing for switching from the low-speed temperature rise control to the high-speed temperature rise control is changed according to the estimated adsorption HC amount. Specifically, the larger the estimated adsorption HC amount, the later the switching timing. As a result, when the amount of adsorbed HC is large, the low-speed temperature rise control can be performed for a longer period of time to desorb more HC, and then the high-speed temperature rise control can be performed. Therefore, it is possible to optimally set the switching timing according to the amount of adsorption HC.

In this way, when the regeneration control is executed, the HC concentration of the exhaust gas from the NOx catalyst 24 can be suppressed to a low level throughout the period, excessive HC emission to the environment can be suppressed, and the generation of white smoke and offensive odor is also suppressed. it can.

When there is an ammonia oxidation catalyst 26 as in the present embodiment, the ECU 100 changes from low speed temperature rise control to high speed so that the HC concentration of the exhaust gas discharged from the ammonia oxidation catalyst 26 does not exceed a predetermined upper limit value when the regeneration control is executed. Set the switching timing to temperature rise control. As a result, it is possible to suppress exhaust gas having an HC concentration exceeding the upper limit value from being discharged to the atmosphere.

FIG. 2 shows a fuel injection method executed per engine cycle (720 ° CA) at each control. The horizontal axis is the crank angle θ (° CA), and each square wave represents the injection time, that is, the injection amount of each injection.

During normal control, as shown in FIG. 2A, the pre-injection Pr and the main injection Mn are executed in this order. During low-speed temperature rise control, as shown in FIG. 2B, pilot injection Pl, pre-injection Pr, main injection Mn, and after-injection Af are executed in this order. As is well known, the after-injection Af is a mode of fuel injection in which the after-injection fuel is incompletely or semi-burned near the combustion end of the main injection fuel to facilitate combustion with the oxidation catalyst 22. The pilot injection Pl may be omitted except when the rotation speed is low and the load is low. A method of injecting three or four fuels in this way is called multi-injection.

During high-speed temperature rise control, as shown in FIG. 2C, pilot injection Pl, pre-injection Pr, main injection Mn, after-injection Af, and post-injection Po are executed in this order. As is well known, the post-injection Po is a mode of fuel injection in which the post-injection fuel is not burned in the cylinder but is completely burned by the oxidation catalyst 22. As a result, the temperature of the filter 23 and the NOx catalyst 24 is raised at a higher speed during the high-speed temperature rise control than during the low-speed temperature rise control. It can be said that the fuel injection method at the time of high-speed temperature rise control is the addition of post-injection to multi-injection. As described above, the exhaust pipe injection by the exhaust pipe injector 38 may be performed instead of the post injection Po.

In the illustrated example, all the injections are executed after the compression top dead center TDC, and the exhaust gas as high as possible is supplied to the oxidation catalyst 22. However, the fuel injection timing can be changed.

Although it is common to both controls, the ECU 100 uses the fuel as shown in FIG. 3A based on the engine speed Ne and the accelerator opening Ac detected by the rotation speed sensor 40 and the accelerator opening sensor 41, respectively. According to the injection amount map, the total injection amount (injection amount for power conversion) of the injection excluding the after injection Af and the post injection Po, particularly the target fuel injection amount Q as the indicated injection amount to the injector 7 is calculated. The fuel injection amount map is set in advance through a test or the like and stored in the ECU 100. A function may be used instead of the map. These points are the same for the map described later. The target fuel injection amount Q is a parameter representing the engine load, and for this parameter, any parameter such as the accelerator opening can be adopted in addition to the target fuel injection amount Q.

Next, FIG. 3B shows whether or not the engine operating state defined by the engine speed Ne and the target fuel injection amount Q is in the first region R1 on the low speed and low load side during normal control. Judgment is made according to the area judgment map as shown in. In the present embodiment, the entire operating region of the engine is divided into a first region R1 and a second region R2 on the higher rotation side or the higher load side. If the detected engine speed Ne and the target fuel injection amount Q are in the first region R1 on the region determination map, the ECU 100 determines that the engine operating state is in the first region R1, and they are in the second region R2. If it is, it is determined that the engine operating state is in the second region R2. The first region R1 of the present embodiment is a region in which the engine speed Ne is equal to or less than a predetermined threshold value N1 and the target fuel injection amount Q is equal to or less than a predetermined threshold value Q1.

The first region R1 is defined in advance as a rotational load region in which the inlet temperature of the NOx catalyst 24 is low and HC is adsorbed on the NOx catalyst 24. On the contrary, the second region R2 is defined in advance as a rotational load region in which the inlet temperature of the NOx catalyst 24 is high and HC is difficult to be adsorbed on the NOx catalyst 24.

Therefore, the amount of HC adsorbed on the NOx catalyst 24 can be estimated by measuring the time during which the engine operating state is in the first region R1 or the mileage. This is because the longer the time or the mileage, the larger the amount of adsorbed HC. Time or mileage can be suitably used as an index value that correlates with the amount of adsorption HC. Although time is used in this embodiment, mileage may be used instead. For convenience, this time is referred to as low load operation time tL.

In the present embodiment, the amount of adsorbed HC is indirectly estimated by measuring the low load operation time tL, but other estimation methods are also possible. For example, the amount of adsorbed HC may be estimated more directly by detecting the difference in HC concentration before and after the NOx catalyst 24 with an HC sensor and integrating the difference in HC concentration.

On the other hand, in the present embodiment, when the estimated adsorption HC amount is equal to or more than a predetermined threshold value, the switching timing is changed according to the estimated adsorption HC amount. In other words, when the estimated adsorption HC amount is less than the threshold value, the switching timing is not changed according to the estimated adsorption HC amount. If the estimated amount of adsorbed HC is small, it is unlikely that the exhaust with a high HC concentration will be discharged to the atmosphere, so there is little practical benefit in delaying the switching timing. Rather, switching to high-speed temperature rise control earlier will end the regeneration control earlier. This is because it is advantageous in terms of fuel efficiency. Therefore, according to the present embodiment, it is possible to advantageously execute the change of the switching timing only when it is necessary.

FIG. 4 shows a change with time of each value when the reproduction control of this embodiment is carried out. In FIG. 4A, line a shows the inlet temperature Tdoc of the oxidation catalyst 22, line b shows the inlet temperature Tdff of the filter 23, and line c shows the inlet temperature Tscr of the NOx catalyst 24. In FIG. 4B, line d shows the HC concentration (referred to as the exhaust HC concentration) C of the exhaust gas discharged from the NOx catalyst 24.

Normal control is executed before the time t1, and the low load operation time tL is measured during this time. Playback control is started at time t1. At the same time as this start, the low-speed temperature rise control is first executed. In the low-speed temperature rise control, multi-injection as shown in FIG. 2B is executed. Of these, the pilot injection Pl, the pre-injection Pr, and the main injection Mn are fuel injections for power generation, and only the after-injection Af is substantially the fuel injection for raising the catalyst temperature. In the early days, not so precise control of the after injection amount was performed. For example, a fixed amount of after injection is continuously injected.

In the case of the illustrated example, at the start of the regeneration control at time t1, the oxidation catalyst inlet temperature Tdoc and the filter inlet temperature Tdpf are substantially the same, while the NOx catalyst inlet temperature TScr is lower than that. When the low-speed temperature rise control is started from this point, the temperatures of the three parties gradually rise at a relatively low speed. While the oxidation catalyst inlet temperature Tdoc and the filter inlet temperature Tdpf rise in almost the same manner, the NOx catalyst inlet temperature TScr rises later than them with a certain time lag due to the influence of the heat capacity of the filter 23.

During this low-speed temperature rise control, the HC adsorbed on the oxidation catalyst 22 and the filter 23 is desorbed and sequentially flowed to the downstream side. On the other hand, the NOx catalyst inlet temperature TScr has not yet reached the HC desorption start temperature Ta due to the influence of the time lag. Therefore, the HC desorbed from the former two is adsorbed by the NOx catalyst 24 and gradually deposited in the NOx catalyst 24. Here, the HC desorption start temperature Ta means the lowest temperature in the temperature range in which HC can be desorbed in the NOx catalyst 24, for example, 200 ° C.

Even if the NOx catalyst inlet temperature TScr reaches the HC desorption start temperature Ta at the subsequent time t3, the low-speed temperature rise control is still continued. As a result, even if HC is desorbed from the NOx catalyst 24, the discharged HC concentration C can be kept low as shown in FIG. 4 (B).

The upper limit value Ch shown in FIG. 4B is an upper limit value of the exhaust HC concentration C that can be processed by the ammonia oxidation catalyst 26. In other words, the HC concentration of the exhaust gas discharged from the ammonia oxidation catalyst 26 is a predetermined upper limit value. It is the maximum value of the exhaust HC concentration C that falls within the following. The value of this upper limit value Ch is set in advance through an actual machine test or the like. As shown in the figure, even if HC is desorbed from the NOx catalyst 24 after time t3, the discharged HC concentration C can be suppressed to the upper limit value Ch or less.

At the subsequent time t4, when the NOx catalyst inlet temperature TScr reaches the switching temperature Tb (> Ta), the control is switched from the low-speed temperature rise control to the high-speed temperature rise control. In the high-speed temperature rise control, as shown in FIG. 2C, the post injection Po is executed in addition to the after injection Af. Since the post-injection fuel is additionally burned in the oxidation catalyst 22, the temperature of the exhaust gas discharged from the oxidation catalyst 22 rises sharply, and the filter inlet temperature Tdpf rises at a high speed from time t4.

After that, after a time lag, the NOx catalyst inlet temperature TScr rises at a high speed from time t5. However, at this point in time, a considerable amount of adsorption HC of the NOx catalyst 24 has already been eliminated and disappeared by the low-speed temperature rise control carried out immediately before time t5, specifically between time t3 and time t4. Therefore, even if the NOx catalyst inlet temperature TScr rises at a high speed, the discharged HC concentration C does not rise sharply in the same manner, and is suppressed to a low value of the upper limit value Ch or less. In this way, it is possible to keep the discharged HC concentration C low even when the high-speed temperature rise control is executed.

The switching temperature Tb is preset as the lowest temperature among the temperatures at which the discharged HC concentration C is equal to or less than the upper limit value Ch even when the high-speed temperature rise control is switched at this temperature. The switching temperature Tb is, for example, 240 ° C.

Here, the method of slow temperature rise control is slightly different before and after the NOx catalyst inlet temperature TScr reaches the HC desorption start temperature Ta. For convenience, the low-speed temperature rise control before reaching the HC desorption start temperature Ta is referred to as early control, and the low-speed temperature rise control after reaching the HC desorption start temperature Ta is referred to as late control.

Further, the time tA between the time t3 and the time t4 when the late control is executed is changed according to the estimated amount of adsorption HC in the NOx catalyst 24. This time tA is called the late control time.

The ECU 100 measures the low load operation time tL, which is an index value of the estimated adsorption HC amount, during normal control before the start of regeneration control. Then, at the same time as the reproduction control is started, the late control time tA is set based on the low load operation time tL. At this time, the ECU 100 calculates the late control time tA corresponding to the low load operation time tL from the time map stored in advance as shown in FIG. 3C. Then, at the time t3 when the NOx catalyst inlet temperature TScr reaches the HC desorption start temperature Ta, the early control is switched to the late control, and then the late control is continued until the set late control time tA elapses.

As shown in FIG. 3C, the longer the low load operation time tL, that is, the larger the estimated adsorption HC amount, the longer the late control time tA is calculated. Therefore, the larger the estimated amount of adsorbed HC, the more adsorbed HC can be slowly desorbed over a long period of time. Therefore, even when the estimated amount of adsorbed HC is large, the amount of adsorbed HC can be reduced to the allowable value or less before the start of the high-speed temperature rise control, and the discharged HC concentration C becomes the upper limit value Ch after switching to the high-speed temperature rise control. Can be reliably suppressed from exceeding.

As described above, in order to suppress the increase in the discharged HC concentration C, it is important to surely reduce the adsorbed HC amount to a certain amount or less in the late control before the high-speed temperature rise control. Therefore, the late control controls the fuel injection amount more precisely than the early control.

That is, after calculating the late control time tA, the ECU 100 sets the target temperature for each time of the NOx catalyst inlet temperature during the late control based on the late control time tA. Then, during the latter stage control, the fuel supply amount to the oxidation catalyst 22 is feedback-controlled so that the actual temperature of the NOx catalyst inlet temperature approaches the target temperature.

FIG. 3D is a graph showing a method of setting the target temperature. The horizontal axis is the late control time tA, and three different late control times tA1 to tA3 are illustrated. tA1 <tA2 <tA3. The vertical axis is the NOx catalyst inlet temperature TScr.

The ECU 100 sets an hourly target temperature within the late control time tA so that the NOx catalyst inlet temperature TScr rises from the HC desorption start temperature Ta to the switching temperature Tb during the late control time tA. Lines a, b, and c in the figure indicate the target temperature for each time corresponding to the late control times tA1, tA2, and tA3, respectively. The longer the late control time tA, that is, the larger the estimated adsorption HC amount, the later the switching timing to the high-speed temperature rise control. Further, the rate of temperature rise of the NOx catalyst inlet temperature TScr is slowed down. The target temperature lines a, b, and c in the illustrated example are straight lines, but are not limited to these, and may be curved lines. In this way, the optimum target temperature for each time can be set according to the magnitude of the amount of adsorbed HC.

The ECU 100 feedback-controls the after-injection amount based on the temperature difference between the two so that the actual temperature of the NOx catalyst inlet temperature TScr detected by the exhaust temperature sensor 44 during the latter-stage control approaches the set target temperature. As a result, the actual temperature can be precisely controlled, and the adsorption HC can be desorbed as scheduled.

Next, more specific control contents of the present embodiment will be described with reference to FIG. The ECU 100 controls according to the procedure shown in the flowchart.

The illustrated flowchart is started at the same time as the reproduction control is started. As described above, the start condition of the reproduction control is that the differential pressure detected by the differential pressure sensor 45 reaches a predetermined upper limit threshold value or more.

On the other hand, in addition to such a filter regeneration request, regeneration control is started based on the NOx catalyst regeneration request. That is, when the time during which the engine is operated in the first region R1, that is, the low load operation time tL becomes long, the HC adsorption amount of the NOx catalyst 24 becomes unacceptably large. In this case, not only the discharged HC concentration C becomes high during regeneration control, but also the NOx catalyst 24 may be poisoned by HC during normal control, and the original purpose of NOx reduction may not be sufficiently achieved. Therefore, in the present embodiment, by performing regeneration control based on the NOx catalyst regeneration request, the adsorption HC is desorbed to regenerate the NOx catalyst 24, and the NOx reduction performance of the NOx catalyst 24 during normal control is sufficiently exhibited. I am trying to do it.

The start condition of the regeneration control based on the NOx catalyst regeneration request is that the low load operation time tL reaches a predetermined upper limit threshold value tLmax or more. The ECU 100 starts the reproduction control when at least one of the two start conditions is satisfied.

When the regeneration control is executed based on the regeneration request of one of the filter 23 and the NOx catalyst 24, the other is also regenerated to no small extent. Therefore, the ECU 100 executes regeneration control in order to regenerate the filter 23 and the NOx catalyst 24.

After the start of the reproduction control, the ECU 100 acquires the value of the low load operation time tL at the start time in step S101. This value is a value measured by the ECU 100 until the start time.

Next, in step S102, the ECU 100 compares the acquired low load operation time tL with a predetermined threshold value tLs. The threshold value tLs is set to a value corresponding to the HC adsorption amount of the NOx catalyst 24, which is so large that it is necessary to perform late control before switching to the high-speed temperature rise control. As a matter of course, the threshold value tLs is a value smaller than the above upper limit threshold value tLmax.

When the low load operation time tL is equal to or greater than the threshold value tLs, the ECU 100 proceeds to step S103 and turns on (ON) a flag indicating that both the early control and the late control in the low speed temperature rise control are performed. Then, the process proceeds to step S104, and the previous term control is executed.

Next, in step S105, the ECU 100 calculates the late control time tA corresponding to the value of the low load operation time tL acquired in step S101 from the map of FIG. 3C. Then, the target temperature for each time corresponding to the late control time tA is set as shown in FIG. 3 (D).

After that, in step S106, the ECU 100 acquires the actual temperature TScr of the NOx catalyst inlet temperature detected by the exhaust temperature sensor 44, and compares this actual temperature TScr with the above-mentioned HC desorption start temperature Ta. If the actual temperature TScr is less than the HC desorption start temperature Ta, the process returns to step S106 to continue the previous period control.

On the other hand, when the actual temperature TScr reaches the HC desorption start temperature Ta or higher, the process proceeds to step S107 to execute the late control. As a result, the low-speed temperature rise control can be switched from the relatively simple early control to the more precise late control.

In the latter-stage control, as described above, the after-injection amount is feedback-controlled, and the actual temperature is accurately increased along the target temperature set in step S105. Therefore, the amount of adsorbed HC of the NOx catalyst 24 can be efficiently reduced in the minimum necessary time while suitably suppressing the discharged HC concentration C during the late control.

Next, in step S108, the ECU 100 compares the actual temperature Tscr of the NOx catalyst inlet temperature with the above-mentioned switching temperature Tb. If the actual temperature Tscr is less than the switching temperature Tb, the process returns to step S108 to continue the late control.

On the other hand, when the actual temperature Tscr reaches the switching temperature Tb or higher, the process proceeds to step S109 to execute high-speed temperature rise control. This adds post-injection and allows the NOx catalyst inlet temperature to rise faster.

After that, the illustrated flowchart ends at the same time as the reproduction control ends. The end condition of the regeneration control is that the differential pressure reaches a predetermined lower limit threshold value or less if the start condition is based on the filter regeneration request, and if the start condition is based on the NOx catalyst regeneration request, for example, high speed. The execution time of the temperature rise control reaches a predetermined threshold value or more.

By the way, when the low load operation time tL is less than the threshold value tLs in step S102, this means that the amount of HC adsorbed by the NOx catalyst 24 is small and there is little need to perform late control before switching to high-speed temperature rise control. To do. Therefore, in this case, the process proceeds to step S110, and the ECU 100 performs normal temperature rise control that directly switches from the early control to the high-speed temperature rise control, omitting the late control.

In this case, as shown in FIG. 4, the high-speed temperature rise control is switched to the high-speed temperature rise control at the time t2, which is a relatively short time after the early control is started at the time t1. This switching timing is significantly earlier than the switching timing t4 from the late control to the high-speed temperature rise control.

As described above, when there is no possibility that the discharged HC concentration C is excessively increased, the high-speed temperature rise control is switched at an early timing, so that the execution time of the regeneration control can be minimized.

As described above, according to the present embodiment, the switching timing (time t4) for switching from the low-speed temperature rise control (late control) to the high-speed temperature rise control according to the estimated adsorption HC amount (low load operation time tL) is set. Since the change is made, it is possible to suppress an increase in the HC concentration of the exhaust gas discharged from the NOx catalyst 24 when the regeneration control is executed.

Further, when the amount of HC adsorbed by the NOx catalyst 24 increases, the NOx catalyst 24 is poisoned by HC and its NOx reduction performance deteriorates. However, according to this embodiment, the adsorbed HC can be desorbed and the NOx catalyst 24 can be regenerated. Therefore, the NOx reduction performance of the NOx catalyst 24 can be maintained satisfactorily.

Further, when the low-speed temperature rise control including the early control and the late control is performed, the temperature of the oxidation catalyst 22 is slowly raised over a relatively long time, so that HC and PM adsorbed on the oxidation catalyst 22 are surely burned and removed. The oxidation catalyst 22 can be regenerated satisfactorily.

As can be understood from the above description, the HC desorption start temperature Ta and the switching temperature Tb of the present embodiment correspond to the first temperature and the second temperature in the claims, and are the latter stages of the present embodiment. The control time tA corresponds to the execution time of the low-speed temperature rise control within the claims.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure can be considered.

(1) For example, the estimated adsorption HC amount, specifically, the value of the low load operation time tL may be corrected by other parameters that affect the adsorption HC amount.

For example, the low load operating time tL may be corrected by the oxidation catalyst inlet temperature Tdoc detected by the exhaust temperature sensor 42. In this case, the lower the oxidation catalyst inlet temperature Tdoc, the easier it is for HC to be adsorbed on the oxidation catalyst 22 and thus the NOx catalyst 24. Therefore, the lower the oxidation catalyst inlet temperature Tdoc, the greater the low load operating time tL. For example, when integrating the low load operation time tL for each calculation cycle, the value obtained by correcting the time per calculation cycle with the oxidation catalyst inlet temperature Tdoc at that time is integrated.

Further, the low load operating time tL may be corrected by the intake air temperature detected by the intake air temperature sensor (not shown). In this case, the lower the intake air temperature, the easier it is for HC to be discharged from the cylinder, and the easier it is for HC to be adsorbed on the NOx catalyst 24. Therefore, the lower the intake air temperature, the larger the low load operation time tL. For example, when integrating the low load operation time tL for each calculation cycle, the value obtained by correcting the time per calculation cycle with the intake air temperature at that time is integrated.

Further, the low load driving time tL may be corrected by the vehicle speed detected by the vehicle speed sensor (not shown). In this case, the lower the vehicle speed, the lower the engine speed and the lower the load, and the more likely the HC is adsorbed on the NOx catalyst 24. Therefore, the lower the vehicle speed, the larger the low load operating time tL. For example, when the low load operation time tL is integrated for each calculation cycle, the value obtained by correcting the time per calculation cycle with the vehicle speed at that time is integrated.

Further, the low load operation time tL may be corrected by the water temperature (temperature of the engine cooling water) detected by the water temperature sensor (not shown). In this case, the lower the water temperature, the easier it is for HC to be discharged from the cylinder, and the easier it is for HC to be adsorbed on the NOx catalyst 24. Therefore, the lower the water temperature, the larger the low load operation time tL. For example, when integrating the low load operation time tL for each calculation cycle, the value obtained by correcting the time per calculation cycle with the water temperature at that time is integrated.

As described above, the value of the low load operating time tL can be corrected by at least one of the oxidation catalyst inlet temperature Tdoc, the intake air temperature, the vehicle speed, and the water temperature. Naturally, such correction is performed by the ECU 100.

(2) Although the start temperature and end temperature of the late control are defined as Ta and Tb by the NOx catalyst inlet temperature TScr in the above embodiment, they may be specified by the filter inlet temperature Tdpf instead. As shown in FIG. 4, the filter inlet temperature Tdpf during regeneration control is higher than the NOx catalyst inlet temperature TScr and rises earlier by the time lag, but except for these points, it rises in the same manner as the NOx catalyst inlet temperature TScr. Is.

(3) Regarding the fuel injection methods shown in FIGS. 2A to 2C, only the main injection Mn is indispensable for power conversion, and the pilot injection Pl and the pre-injection Pr may be omitted as appropriate.

(4) In FIG. 3C, the line showing the relationship between the low load operation time tL and the late control time tA is a straight line, but the line may be a curved line.

(5) In FIG. 3B, the first region R1 is simply defined by two straight lines representing Ne = N1 and Q = Q1, but the first region R1 is not limited to this, and a more complicated straight line or curve or the like is used. The first region R1 may be defined.

(6) In the above embodiment, the oxidation catalyst 22, the filter 23, the selective reduction NOx catalyst 24 and the ammonia oxidation catalyst 26 are provided in this order from the upstream side, but at least one of the filter 23 and the ammonia oxidation catalyst 26 can be omitted. Further, one or more SOF catalysts may be provided instead of the filter 23. The SOF catalyst removes an organic soluble component (SOF (Soluble Organic Fraction)) contained in PM.

The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the scope of claims are included in the present disclosure. Therefore, this disclosure should not be construed in a limited way and can be applied to any other technique that belongs within the scope of the ideas of this disclosure.

1 Internal combustion engine (engine)
4 Exhaust passage 7 Injector 22 Oxidation catalyst 23 Filter 24 NOx catalyst 26 Ammonia oxidation catalyst 38 Exhaust pipe injector 42, 43, 44 Exhaust temperature sensor 100 Electronic control unit (ECU)

Claims (9)

Oxidation catalyst and selective reduction NOx catalyst provided in order from the upstream side in the exhaust passage of the internal combustion engine,
A control unit configured to perform regeneration control to raise the temperature of the exhaust,
With
The control unit
The amount of adsorbed HC of the NOx catalyst is estimated when the regeneration control is not executed.
When the regeneration control is executed, after performing the low-speed temperature rise control for raising the temperature of the exhaust gas at a low speed, the high-speed temperature rise control for raising the temperature of the exhaust gas at a high speed is performed, and the low-speed temperature rise control is performed according to the estimated adsorption HC amount. An exhaust gas purification device for an internal combustion engine, which is characterized by changing the switching timing for switching from to high-speed temperature rise control. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the control unit delays the switching timing as the estimated adsorption HC amount increases. The exhaust gas purification device for an internal combustion engine according to claim 1 or 2, wherein the control unit changes the switching timing according to the estimated adsorption HC amount when the estimated adsorption HC amount is equal to or higher than a predetermined threshold value. The control unit
Low-speed temperature rise control is performed until the inlet temperature of the NOx catalyst rises from a predetermined first temperature to a second temperature, and when the inlet temperature of the NOx catalyst reaches the second temperature, low-speed temperature rise control is performed. Switch to high-speed temperature rise control,
The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the larger the estimated amount of adsorbed HC, the longer the execution time of the low-speed temperature rise control. The control unit stores in advance a map that defines the relationship between the adsorption HC amount and the execution time of the low-speed temperature rise control, and calculates the execution time of the low-speed temperature rise control corresponding to the estimated adsorption HC amount from the map. The exhaust purification device for an internal combustion engine according to claim 4. The control unit sets an hourly target temperature of the NOx catalyst inlet temperature during the low-speed temperature rise control based on the execution time of the low-speed temperature rise control, and the actual inlet temperature of the NOx catalyst during the low-speed temperature rise control. The exhaust gas purification device for an internal combustion engine according to claim 4 or 5, wherein the fuel supply amount to the oxidation catalyst is feedback-controlled so that the temperature approaches the target temperature. The control unit causes the in-cylinder injector to execute after-injection during the low-speed temperature rise control, and additionally causes the in-cylinder injector to execute post-injection in addition to the after-injection during the high-speed temperature rise control, or the exhaust pipe. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 6, wherein the injector is made to perform exhaust pipe injection. Further provided with another oxidation catalyst provided in the exhaust passage on the downstream side of the NOx catalyst.
The control unit sets the switching timing from the low-speed temperature rise control to the high-speed temperature rise control so that the HC concentration of the exhaust gas discharged from the other oxidation catalyst does not exceed a predetermined upper limit value when the regeneration control is executed. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 7. It is a control method of an internal combustion engine provided with an oxidation catalyst and a selective reduction NOx catalyst provided in order from the upstream side in the exhaust passage.
The first step of estimating the amount of adsorbed HC of the NOx catalyst when the regeneration control for raising the temperature of the exhaust gas is not executed, and
When the regeneration control is executed, the low-speed temperature rise control for raising the temperature of the exhaust at a low speed is performed, and then the high-speed temperature rise control for raising the temperature of the exhaust at a high speed is performed, and the low-speed temperature rise control is performed according to the estimated adsorption HC amount. The second step of changing the switching timing to switch from to high-speed temperature rise control,
A control method for an internal combustion engine, which is characterized by being equipped with.

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