JP2008223592A - Exhaust emission control device of internal-combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal-combustion engine capable of promoting the dispersion of a reducing agent while a drop of the engine operating performance is suppressed. <P>SOLUTION: The exhaust emission control device of the internal-combustion engine is equipped with an exhaust emission cleaning catalyst installed in the exhaust passage of the internal-combustion engine, a reducing agent supplying means to supply the reducing agent into the exhaust gas existing upstream of the catalyst, an exhaust gas throttle valve located upstream of the exhaust emission control device and downstream of the reducing agent supplying means, a target throttle pressure setting means to decide the target pressure in the exhaust passage upstream of the exhaust gas throttle valve when the reducing agent is supplied by the supplying means (S102, S105), and an exhaust gas throttle valve control means to adjust the opening of the exhaust gas throttle valve so that the pressure in the exhaust passage upstream of the exhaust gas throttle valve becomes the target pressure (S103), which is conducted simultaneously with the reducing agent being supplied by the supplying agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present. Then, by adding a reducing agent (for example, fuel) into the exhaust gas upstream of the NOx catalyst, the NOx stored in the NOx catalyst can be reduced.

  In order to reduce NOx in this way, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst due to fuel injection or the like must be made a rich air-fuel ratio. However, when fuel is injected into the exhaust, the fuel adheres to the wall surface of the exhaust passage, so that there is a possibility that the air-fuel ratio of the exhaust does not become rich or the fuel becomes difficult to diffuse. As a result, the amount of reducing agent that is wasted increases, so that a larger amount of reducing agent is required, and the consumption of the reducing agent increases.

Here, a reducing agent addition valve, an exhaust throttle valve, and a NOx catalyst are provided in this order from the upstream side of the exhaust passage, and the exhaust throttle valve is closed during addition of the reducing agent to increase the flow velocity of the exhaust gas near the exhaust passage wall surface. The fuel adhering to the fuel can be blown away (see, for example, Patent Document 1).
JP 2003-269147 A JP-A-2005-76604

  However, when the exhaust throttle valve is closed, the back pressure increases particularly during high-load operation of the internal combustion engine, so that the performance of the internal combustion engine may be degraded due to an increase in pump loss, and fuel consumption may be deteriorated.

  The present invention has been made in view of the above-described problems, and provides a technique capable of promoting the diffusion of a reducing agent while suppressing a decrease in the performance of an internal combustion engine in an exhaust purification device for an internal combustion engine. For the purpose.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
An exhaust purification catalyst for purifying exhaust gas provided in an exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the exhaust purification catalyst;
An exhaust throttle valve that is provided upstream of the exhaust purification device and downstream of the reducing agent supply means and adjusts the flow passage area of the exhaust passage;
Target throttle pressure setting means for determining a target pressure in the exhaust passage upstream of the exhaust throttle valve when the reducing agent is supplied by the reducing agent supply means;
An exhaust throttle that adjusts the opening of the exhaust throttle valve so that the pressure in the exhaust passage upstream of the exhaust throttle valve becomes the target pressure as the reducing agent is supplied by the reducing agent supply means. Valve control means;
It is characterized by providing.

The exhaust purification catalyst purifies exhaust by supplying a reducing agent from the reducing agent supply means, or recovers the exhaust purification capability. Further, when the exhaust throttle valve is closed, the load on the internal combustion engine increases, so that the exhaust temperature rises. Thereby, the exhaust purification catalyst can be activated, the reaction rate at the exhaust purification catalyst can be increased, and evaporation of the reducing agent can be promoted. The temperature of the exhaust purification catalyst can be adjusted by adjusting the opening of the exhaust throttle valve.

  Further, closing the exhaust throttle valve increases the pressure of the exhaust upstream of the exhaust throttle valve. For this reason, the momentum of the reducing agent supplied from the reducing agent supply means is weakened. As a result, the amount of reducing agent adhering to the wall surface of the exhaust passage is reduced, so that the reducing agent quickly reaches the exhaust purification catalyst. Further, the reducing agent evaporates and diffuses in the exhaust gas, so that the reducing agent is distributed and supplied over a wide range of the exhaust purification catalyst.

  Then, the target throttle pressure setting means determines the exhaust pressure required at that time as the target pressure. The target pressure is determined in consideration of promoting the diffusion of the reducing agent or increasing the temperature of the exhaust gas, and suppressing the performance deterioration of the internal combustion engine. That is, the higher the target pressure is, the more the diffusion of the reducing agent is promoted and the temperature of the exhaust gas is higher. Therefore, the target pressure is set to the minimum necessary height. The target throttle pressure setting means may determine a target value of the differential pressure between the upstream side and the downstream side of the exhaust throttle valve.

  Further, “in accordance with the supply of the reducing agent by the reducing agent supply means” may be simultaneous with the supply of the reducing agent, and the exhaust pressure is the target pressure when the reducing agent is supplied. Further, it may be before supply of the reducing agent. Alternatively, the supply of the reducing agent may be completed or the reducing agent may pass through the exhaust throttle valve.

  In this way, by determining the target pressure and adjusting the opening of the exhaust throttle valve so that the actual pressure becomes the target pressure in accordance with the supply of the reducing agent, the deterioration of the performance of the internal combustion engine is suppressed. The diffusion of the reducing agent can be promoted. If the diffusion of the reducing agent is promoted, the consumption of the reducing agent is reduced.

  In the present invention, the target throttle pressure setting means can determine the target pressure based on the exhaust temperature.

  By adjusting the opening of the exhaust throttle valve, the exhaust temperature can be raised to a required value. The required value of the exhaust temperature may be, for example, the activation temperature of the exhaust purification catalyst, or may be the temperature that diffuses throughout the exhaust purification catalyst. That is, when the exhaust temperature is lower than the required value, the exhaust temperature can be increased to the required value by reducing the opening of the exhaust throttle valve.

  Since the exhaust temperature rises as the opening of the exhaust throttle valve is reduced, the temperature of the exhaust purification catalyst can be further increased or the diffusion of the reducing agent can be promoted. Then, by determining the opening of the exhaust throttle valve according to the required value of the exhaust temperature and the actual exhaust temperature, the closing amount of the exhaust throttle valve can be made the minimum necessary amount. Therefore, an increase in pump loss can be suppressed.

  In addition, when the temperature of the exhaust gas is high, such as during high-load operation of the internal combustion engine, the temperature of the exhaust gas purification catalyst is maintained high, and further diffusion of the reducing agent is promoted, so it is not necessary to increase the target pressure. Absent. That is, the target pressure can be lowered as the temperature of the exhaust gas increases.

  In the present invention, the target throttle pressure setting means can further determine the target pressure based on the intake air amount of the internal combustion engine.

  When the intake air amount of the internal combustion engine increases, the diffusion of the reducing agent is further promoted, so that the reducing agent can be diffused even if the target pressure is lowered. That is, the target pressure can be lowered as the intake air amount of the internal combustion engine increases. By doing in this way, since a target pressure can be set to minimum required height, the increase in pump loss can be suppressed.

  In the present invention, the target throttle pressure setting means can determine the target pressure based on the ease of diffusion of the reducing agent.

  That is, when the reducing agent is difficult to diffuse (for example, when the temperature of the exhaust gas is low or when the amount of intake air is small), the diffusion of the reducing agent can be promoted by increasing the target pressure.

  Further, when the temperature of the exhaust purification catalyst is equal to or higher than a predetermined temperature (for example, the activation temperature), the more the diffusion of the reducing agent proceeds, the lower the target pressure is set in the exhaust purification catalyst. Can be suitably supplied. And the increase in pump loss can be suppressed by determining a target pressure according to the ease of spreading | diffusion of a reducing agent.

  In the present invention, when the temperature of the exhaust gas of the internal combustion engine is lower than a predetermined temperature, the pressure in the exhaust passage is equal to the target pressure regardless of whether or not the reducing agent is supplied by the reducing agent supply means. The exhaust passage is adjusted so that the reducing agent is supplied by the reducing agent supply means when the exhaust temperature of the internal combustion engine is equal to or higher than a predetermined temperature. The opening of the exhaust throttle valve can be adjusted so that the internal pressure becomes the target pressure.

  The predetermined temperature may be, for example, the activation temperature of the exhaust purification catalyst, or the temperature at which the reducing agent is diffused throughout the exhaust purification catalyst, similar to the required value. Moreover, it is good also as temperature required in order to keep the temperature of an exhaust purification catalyst more than activation temperature.

  That is, when the exhaust temperature is lower than a predetermined temperature, it is necessary to increase the exhaust temperature. On the other hand, the exhaust purification catalyst can be maintained at a predetermined temperature or higher by adjusting the opening of the exhaust throttle valve so that the pressure upstream of the exhaust throttle valve is always the target pressure. When the temperature of the exhaust gas is lower than the predetermined temperature, the load on the internal combustion engine is often low and the back pressure is unlikely to increase, so the degree of performance deterioration of the internal combustion engine is small.

  On the other hand, when the temperature of the exhaust gas is equal to or higher than a predetermined temperature, the target pressure is determined mainly to promote the diffusion of the reducing agent. That is, when the exhaust pressure is increased by closing the exhaust throttle valve, the reducing agent's momentum is weakened and the reducing agent diffuses more. By promoting the diffusion of the reducing agent in this way, the amount of reducing agent supplied can be reduced.

  In order to promote the diffusion of the reducing agent, it is only necessary that the exhaust pressure be the target pressure when the reducing agent is supplied. That is, when the reducing agent is not supplied, it is not necessary to set the exhaust pressure to the target pressure. Further, when the temperature of the exhaust gas is equal to or higher than a predetermined temperature, the back pressure tends to increase because the load on the internal combustion engine is often high. On the other hand, an increase in pump loss can be minimized by setting the exhaust pressure to the target pressure in accordance with the supply of the reducing agent and opening the exhaust throttle valve when the reducing agent is not supplied.

  ADVANTAGE OF THE INVENTION According to this invention, spreading | diffusion of a reducing agent can be promoted, suppressing the performance fall of an internal combustion engine.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and an intake / exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. An air flow meter 4 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake passage 2 is provided in the middle of the intake passage 2. The air flow meter 4 measures the intake air amount of the internal combustion engine 1. Further, the amount of exhaust gas can be obtained based on the intake air amount.

On the other hand, an exhaust throttle valve 5 and an NOx storage reduction catalyst 6 (hereinafter referred to as NOx catalyst 6) are provided in the exhaust passage 3 in order from the upstream side. The NOx catalyst 6 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have In this embodiment, the NOx catalyst 6 corresponds to the exhaust purification catalyst in the present invention. The exhaust purification catalyst may be a catalyst to which a reducing agent is supplied, and may be, for example, a selective reduction type NOx catalyst.

  The exhaust passage 3 upstream of the exhaust throttle valve 5 is provided with a reducing agent supply valve 7 for injecting fuel (light oil) as a reducing agent into the exhaust gas flowing through the exhaust passage 3. The reducing agent supply valve 7 is opened by a signal from the ECU 10 described later and injects fuel into the exhaust. In this embodiment, the reducing agent supply valve 7 corresponds to the reducing agent supply means in the present invention.

Further, an exhaust temperature sensor 8 for detecting the temperature of the exhaust gas flowing through the exhaust passage 3 is attached to the exhaust passage 3 downstream of the exhaust throttle valve 5 and upstream of the NOx catalyst 6.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit 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.

  In addition to the above sensors, the ECU 10 is connected to an accelerator opening sensor 12 for detecting the amount of depression of the accelerator pedal 11 via electrical wiring, and the output signals of these sensors are input. The accelerator opening sensor 12 can detect the load of the internal combustion engine 1. On the other hand, the exhaust throttle valve 5 and the reducing agent supply valve 7 are connected to the ECU 10 via electric wiring, and these devices are controlled by the ECU 10.

  In this embodiment, when the temperature of the exhaust gas is lower than the predetermined temperature, the exhaust throttle valve 5 is set to the closed side rather than fully opened regardless of whether or not the reducing agent is supplied from the reducing agent supply valve 7. On the other hand, when the temperature of the exhaust gas is equal to or higher than a predetermined temperature, the exhaust throttle valve 5 is set to the closed side rather than being fully opened when the reducing agent is supplied from the reducing agent supply valve 7. That is, when the exhaust temperature is equal to or higher than the predetermined temperature and the reducing agent is not supplied, the exhaust throttle valve 5 is fully opened. In this embodiment, the predetermined temperature is the activation temperature of the NOx catalyst 6.

At this time, the target value of the exhaust pressure is determined based on the target value of the exhaust temperature and the ease of diffusion of the reducing agent, and the opening of the exhaust throttle valve 5 is adjusted so that the actual exhaust pressure becomes the target value. Is determined.
By doing in this way, since the raise of the exhaust pressure can be suppressed to the necessary minimum, an increase in pump loss can be suppressed.

  Here, as the exhaust gas temperature is higher and the intake air amount of the internal combustion engine 1 is increased, the reducing agent supplied from the reducing agent supply valve 7 is more easily evaporated, so that the diffusion of the reducing agent is further promoted. That is, the target value of the exhaust pressure can be reduced as the exhaust temperature is higher or the intake air amount of the internal combustion engine 1 is increased. For this reason, in this embodiment, a value obtained by multiplying the exhaust temperature by the intake air amount is used as a value representing the ease of diffusion of the reducing agent, and the target value of the exhaust pressure is determined based on this value. The intake air amount of the internal combustion engine 1 may be the amount of exhaust.

  Here, FIG. 2 is a time chart showing an example of the relationship between the vehicle speed, the injection pulse of the reducing agent supply valve 7, and the opening degree of the exhaust throttle valve 5. The vehicle speed may be the load of the internal combustion engine 1 or the exhaust temperature. The supply of the reducing agent from the reducing agent supply valve 7 is repeatedly executed every predetermined time.

  When the vehicle speed is slower than the threshold value (period A and period B to C), the exhaust throttle valve is closed regardless of whether or not the reducing agent is supplied from the reducing agent supply valve 7. Is done. Further, when the vehicle speed is equal to or higher than the threshold value (period from A to B and after C), the exhaust throttle valve 5 is fully opened as the reducing agent is supplied from the reducing agent supply valve 7. Is also closed.

During low load operation of the internal combustion engine 1, the exhaust throttle valve 5 is kept closed because the exhaust temperature is low, and the exhaust temperature is raised. As a result, the NOx catalyst 6 can be maintained at the activation temperature or higher, so that NOx is purified when the reducing agent is supplied from the reducing agent supply valve 7.
That is, the threshold value at the vehicle speed is a temperature at which the temperature of the NOx catalyst 6 can be set to a predetermined temperature or higher, and may be a value at which the exhaust temperature becomes a predetermined temperature.

On the other hand, since the temperature of the exhaust gas is high during high load operation, the exhaust throttle valve 5 is closed rather than fully opened only when the reducing agent is supplied from the reducing agent supply valve 7. That is, when the temperature of the exhaust gas is equal to or higher than the predetermined temperature, the temperature of the NOx catalyst 6 is sufficiently high, and after that, it is only necessary to promote the diffusion of the reducing agent. Therefore, it is not always necessary to close the exhaust throttle valve 5 with respect to the fully opened state, and the exhaust throttle valve 5 may be closed in accordance with the supply of the reducing agent.

  Here, the degree of opening when the exhaust throttle valve 5 is closed from the fully open position is determined by the target value of the exhaust pressure as described above.

  FIG. 3 is a flowchart showing a control flow of the exhaust throttle valve 5 according to this embodiment. This routine is repeatedly executed at specified time intervals.

  In step S101, it is determined whether there is a request to increase the exhaust gas temperature. For example, when the temperature of the NOx catalyst 6 is lower than the activation temperature, or when it is estimated that the load of the internal combustion engine 1 is low and the temperature of the NOx catalyst 6 is lower than the activation temperature, a request for increasing the exhaust temperature is made.

  If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, the process proceeds to step S104.

In step S102, a target value of the exhaust pressure is calculated. FIG. 4 is a diagram showing the relationship between the target increase value of the exhaust temperature and the target value of the exhaust pressure. The target exhaust gas temperature increase value indicates the difference between the predetermined temperature and the current exhaust gas temperature, and is a value indicating how much the exhaust gas temperature must be increased. In this step, the target value of the exhaust pressure is increased as the target increase value of the exhaust temperature increases.

  In step S103, the opening of the exhaust throttle valve 5 is set based on the target value of the exhaust pressure. The relationship between the target value of the exhaust pressure and the opening of the exhaust throttle valve 5 may be obtained in advance by experiments or the like, or feedback control may be performed by actually measuring the exhaust pressure. In this embodiment, the ECU 10 that executes the process of step S103 corresponds to the exhaust throttle valve control means in the present invention.

In step S104, it is determined whether or not there is a reducing agent supply request from the reducing agent supply valve 7. When it is necessary to supply the reducing agent to the NOx catalyst 6, a reducing agent supply request is made. For example, a reducing agent supply request is made at predetermined time intervals or when a specified amount of NOx is occluded in the NOx catalyst 6. In this routine, the opening of the exhaust throttle valve 5 is adjusted before the reducing agent is injected in order to set the exhaust pressure to the target value before the reducing agent is injected from the reducing agent supply valve 7.

  If an affirmative determination is made in step S104, the process proceeds to step S105, whereas if a negative determination is made, the process proceeds to step S106.

  In step S105, a target value of the exhaust pressure is calculated. Unlike the process in step S102, the target value of the exhaust pressure is calculated based on the value obtained by multiplying the exhaust temperature by the intake air amount. That is, in this step, since the temperature of the NOx catalyst 6 is sufficiently high, the target value of the exhaust pressure is calculated mainly for promoting the diffusion of the reducing agent rather than increasing the temperature of the NOx catalyst 6.

  FIG. 5 is a graph showing the relationship between the value obtained by multiplying the exhaust temperature by the intake air amount and the target value of the exhaust pressure. The larger the value obtained by multiplying the exhaust air temperature by the intake air amount, the more the diffusion of the reducing agent is promoted. Therefore, the target value of the exhaust pressure is reduced.

  In this embodiment, the ECU 10 that executes the process of step S102 or step S105 corresponds to the target throttle pressure setting means in the present invention.

  In step S106, the exhaust throttle valve 5 is fully opened. That is, it is not necessary to close the exhaust throttle valve 5 because the exhaust temperature is high, and it is not necessary to promote the diffusion of the reducing agent because no reducing agent is supplied. Further, when the exhaust throttle valve 5 is closed, the pump loss increases, so the exhaust throttle valve 5 is fully opened.

Thus, when the exhaust gas temperature is lower than the predetermined temperature, the exhaust throttle valve 5 is always closed rather than fully opened, thereby increasing the temperature of the NOx catalyst 6 and promoting the diffusion of the reducing agent. Is possible. In addition, when the exhaust gas temperature is equal to or higher than a predetermined temperature, the exhaust throttle valve 5 is closed from the fully open state in accordance with the supply of the reducing agent, thereby reducing the diffusion of the reducing agent while suppressing an increase in pump loss. Can be promoted.

As described above, according to this embodiment, the temperature of the NOx catalyst 6 is maintained at the activation temperature or higher,
Moreover, since the diffusion of the reducing agent can be promoted, the NOx purification rate can be increased. Moreover, the supply amount of the reducing agent can be reduced. Furthermore, since the exhaust throttle valve 5 is closed only when necessary, an increase in pump loss can be suppressed, so that deterioration in fuel consumption can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is the time chart which showed an example of the relationship between a vehicle speed, the injection pulse of a reducing agent supply valve, and the opening degree of an exhaust throttle valve. It is the flowchart which showed the flow of control of the exhaust throttle valve by an Example. It is the figure which showed the relationship between the target raise value of exhaust temperature, and the target value of exhaust pressure. It is the figure which showed the relationship between the value which multiplied the amount of intake air to exhaust temperature, and the target value of exhaust pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake passage 3 Exhaust passage 4 Air flow meter 5 Exhaust throttle valve 6 Occlusion reduction type NOx catalyst 7 Reductant supply valve 8 Exhaust temperature sensor 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor

Claims (5)

An exhaust purification catalyst for purifying exhaust gas provided in an exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the exhaust purification catalyst;
An exhaust throttle valve that is provided upstream of the exhaust purification device and downstream of the reducing agent supply means and adjusts the flow passage area of the exhaust passage;
Target throttle pressure setting means for determining a target pressure in the exhaust passage upstream of the exhaust throttle valve when the reducing agent is supplied by the reducing agent supply means;
An exhaust throttle that adjusts the opening of the exhaust throttle valve so that the pressure in the exhaust passage upstream of the exhaust throttle valve becomes the target pressure as the reducing agent is supplied by the reducing agent supply means. Valve control means;
An exhaust emission control device for an internal combustion engine, comprising:   The exhaust purification device for an internal combustion engine according to claim 1, wherein the target throttle pressure setting means determines the target pressure based on an exhaust temperature.   The exhaust purification device for an internal combustion engine according to claim 2, wherein the target throttle pressure setting means further determines the target pressure based on an intake air amount of the internal combustion engine.   The exhaust purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the target throttle pressure setting means determines the target pressure based on ease of diffusion of the reducing agent.   When the temperature of the exhaust gas of the internal combustion engine is lower than a predetermined temperature, the pressure in the exhaust passage becomes the target pressure regardless of whether or not the reducing agent is supplied by the reducing agent supply means. The opening of the exhaust throttle valve is adjusted, and when the temperature of the exhaust gas of the internal combustion engine is equal to or higher than a predetermined temperature, the pressure in the exhaust passage is adjusted as the reducing agent is supplied by the reducing agent supply means. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the opening degree of the exhaust throttle valve is adjusted so as to be a target pressure.

Images