JP4645586B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  As a technique for purifying exhaust gas discharged from an internal combustion engine, a NOx catalyst (for example, a storage reduction type NOx catalyst, a selective reduction type NOx catalyst, etc.) for purifying nitrogen oxide (NOx) contained in the exhaust gas, There is known an exhaust purification system including an exhaust purification device such as a filter for collecting particulate matter contained therein.

  By the way, there is a case where a temperature increase request for quickly raising the temperature of the exhaust purification device to a predetermined required temperature is issued to the exhaust purification system including the exhaust purification device. For example, when the temperature of the NOx catalyst is lower than the activation temperature, it is necessary to quickly raise it to the activation temperature. Further, when the SOx poisoning recovery control for the NOx catalyst is performed, it is necessary to maintain the NOx catalyst at a high temperature (for example, 600 ° C. to 650 ° C.). In addition, when performing PM regeneration control for oxidizing and removing PM collected by the filter, it is necessary to raise the temperature of the filter to a temperature at which PM can be oxidized (combusted) (for example, 500 ° C. to 700 ° C.). is there.

There has also been proposed an exhaust purification system that includes a bypass passage capable of bypassing the NOx catalyst in the exhaust discharged from the internal combustion engine and can adjust the flow rate of the exhaust gas passing through the bypass passage based on the operating state. (For example, see Patent Document 1).
JP-A-6-10656 JP 2006-153000 A

  However, the above prior art does not disclose a technique for quickly raising the temperature of the exhaust purification device. Further, when the temperature raising control is performed on the exhaust purification device, the temperature of the exhaust purification device is reduced due to the removal of heat by the exhaust passing through the exhaust purification device or the large heat capacity of the exhaust purification device. In some cases, it is difficult to quickly increase the temperature to a predetermined required temperature.

  The present invention has been made in view of the above prior art, and an object of the present invention is to quickly raise the temperature of an exhaust purification device provided in an exhaust passage of an internal combustion engine to a target temperature required for the exhaust purification device. It is to provide technology that can do.

  In order to achieve the above object, the present invention reduces the flow rate passing through the pre-stage catalyst and adds a reducing agent to the reducing agent supply means when raising the temperature of the exhaust purification device to a target temperature required for the exhaust purification device. The greatest feature is that after the temperature of the front catalyst is raised by supplying it to the front catalyst, the amount of heat is supplied from the front catalyst to the exhaust purification device via the exhaust gas by increasing the flow rate passing through the front catalyst.

More specifically, an exhaust passage that is connected at one end to the internal combustion engine and through which the exhaust from the internal combustion engine passes,
A pre-stage catalyst provided in the exhaust passage and having an oxidation function;
An exhaust purification device that is provided downstream of the preceding catalyst in the exhaust passage and purifies exhaust;
A reducing agent supply means that is provided upstream of the preceding catalyst and supplies a reducing agent to the preceding catalyst and the exhaust purification device;
A bypass passage for communicating the upstream portion of the exhaust passage with respect to the reducing agent supply means and the downstream portion of the upstream catalyst, and bypassing the upstream catalyst to the exhaust gas passing through the exhaust passage;
Catalyst side reduction control for increasing the bypass side flow rate, which is the flow rate of the exhaust gas passing through the bypass passage, and decreasing the catalyst side flow rate, which is the flow rate of the exhaust gas passing through the preceding catalyst, and reducing the bypass side flow rate And an exhaust flow rate changing means capable of performing catalyst side increase control for increasing the catalyst side flow rate,
With
When raising the temperature of the exhaust gas purification device to a target temperature required for the exhaust gas purification device, causing the exhaust gas flow rate changing means to execute the catalyst side reduction control and causing the reducing agent supply means to supply the reducing agent. After the temperature of the preceding catalyst is raised to a predetermined temperature that can be raised in the subsequent stage, the exhaust flow rate changing means is caused to execute the catalyst side increase control.

  In the exhaust purification system having the above configuration, the temperature of the front catalyst is raised by the reaction heat generated when the reducing agent supplied by the reducing agent supply means is oxidized in the front catalyst. Then, the exhaust gas discharged from the internal combustion engine is heated at the pre-stage catalyst, and the exhaust gas that has reached a high temperature flows into the exhaust gas purification device on the downstream side, so that the exhaust gas purification device reaches the target temperature required for the exhaust gas purification device. The temperature is raised.

  By the way, in order to quickly raise the temperature of the exhaust purification device to the target temperature, it is necessary to give more heat to the upstream catalyst. If it does so, the temperature of a front | former stage catalyst will rise to a higher temperature, and can heat-up the downstream exhaust gas purification apparatus more efficiently. However, if the flow rate on the catalyst side, which is the flow rate of the exhaust gas that passes through the pre-stage catalyst when the reductant is supplied by the reductant supply means, is large, the amount of heat removed by the exhaust increases, and the temperature of the pre-stage catalyst rises quickly It may not be possible to

  In contrast, in the present invention, the catalyst-side flow rate can be increased or decreased by causing the exhaust flow rate changing means to perform the catalyst-side decrease control and the catalyst-side increase control. In the present invention, when the temperature of the exhaust gas purification device is raised to the target temperature required for the exhaust gas purification device, the exhaust gas flow rate changing means is caused to execute the catalyst side reduction control. As a result, the bypass side flow rate, which is the flow rate of the exhaust gas passing through the bypass passage, can be increased and the catalyst side flow rate can be decreased.

  Then, by causing the reducing agent supply means to supply the reducing agent to the pre-stage catalyst while causing the exhaust flow rate changing means to execute the catalyst side reduction control, the temperature of the pre-stage catalyst can be quickly raised to the post-stage while suppressing the removal of heat due to the exhaust. The temperature can be raised to a possible temperature. Here, the temperature that can be raised at the rear stage is required for the front stage catalyst that is required to cause the exhaust gas that is heated when passing through the front stage catalyst to flow into the exhaust purification apparatus and raise the temperature of the exhaust purification apparatus to the target temperature. Temperature.

  In the present invention, as described above, after the upstream catalyst has been heated to the temperature capable of increasing the subsequent stage, the exhaust flow rate changing means is caused to execute the catalyst side increase control. That is, the bypass side flow rate is decreased and the catalyst side flow rate is increased. As a result, the flow rate of the exhaust gas that passes through the front catalyst and the exhaust gas purification device on the downstream side of the front catalyst increases. As a result, the amount of heat can be suitably transmitted from the pre-stage catalyst to the exhaust gas purification device via the exhaust gas that has passed through the pre-stage catalyst and has reached a high temperature. Therefore, the exhaust purification device can be rapidly heated to the target temperature.

Further, in the present invention, when the temperature of the exhaust purification device is raised to the target temperature by the catalyst side increase control after the temperature of the upstream catalyst is raised to the temperature that can be heated to the downstream side, the reducing agent is supplied to the reducing agent supply means. It may be stopped. In that case, it is only necessary to raise the temperature of the preceding catalyst so that the exhaust purification device raises the temperature to the target temperature even if the reducing agent is not supplied when the catalyst side increase control is performed. Thereby, the supply amount of the reducing agent by the reducing agent supply means can be saved. That is, it is possible to reduce as much as possible the amount of reducing agent consumed to raise the temperature of the exhaust purification device to the target temperature. Further, when the reducing agent supply means continues to supply the reducing agent when the catalyst side increase control is executed, it is possible to raise the temperature of the exhaust purification device more quickly to the target temperature.

  In the present invention, it is more preferable that the exhaust flow rate changing means makes the flow rate on the catalyst side substantially zero until the temperature of the front catalyst rises to the temperature that can be raised at the rear stage in the catalyst side reduction control. . As a result, the amount of heat removed from the pre-stage catalyst by the exhaust gas passing through the pre-stage catalyst can be reduced as much as possible, and the pre-stage catalyst can be quickly raised to a temperature capable of raising the post-stage catalyst.

  In the catalyst side increase control, it is more preferable that the flow rate on the bypass side is made substantially zero after the temperature of the upstream catalyst is raised to the temperature that can be raised in the subsequent stage. Thereby, more exhaust gas which became high temperature can be made to flow into an exhaust gas purification apparatus. That is, it becomes possible to raise the temperature of the exhaust purification device to the target temperature as quickly as possible.

  In the present invention, the target temperature of the exhaust purification device may be set to various different temperatures as required. For example, when the exhaust purification device has a NOx catalyst that can reduce NOx in the exhaust (for example, a NOx storage reduction catalyst, a selective reduction NOx catalyst, etc.), the target temperature may be the activation temperature of the NOx catalyst. . That is, when the temperature of the NOx catalyst is lower than the activation temperature, the NOx catalyst may be activated quickly according to the present invention. This is because when the catalyst is not active, the NOx purification rate in the NOx catalyst is remarkably lowered and the emission is deteriorated.

  Further, in the case of the above configuration, when performing SOx poisoning recovery control for recovering the NOx catalyst poisoned by SOx in the exhaust, it is necessary to maintain the NOx catalyst at a high temperature (for example, 600 ° C. to 650 ° C.). is there. In that case, the target temperature may be a temperature at which SOx can be reduced from the NOx catalyst.

  Further, when the exhaust purification device has a filter capable of collecting particulate matter in the exhaust (hereinafter also simply referred to as “PM”), the target temperature is a temperature at which PM can be oxidized (combusted) (for example, 500 ° C. to 700 ° C.).

  In addition, as described above, the bypass passage in the present invention communicates the upstream portion of the exhaust passage with respect to the reducing agent supply means and the downstream portion of the upstream catalyst, and bypasses the upstream oxidation catalyst to the exhaust gas. Here, the “portion on the downstream side of the upstream catalyst” communicating with one end of the bypass passage may be a portion on the upstream side of the exhaust purification device in the exhaust passage, or a portion on the downstream side of the exhaust purification device.

  By the way, since the operating state of the internal combustion engine is changed at any time, the temperature of exhaust gas discharged from the internal combustion engine and the flow rate of exhaust gas change according to the operating state (for example, engine load, engine speed, etc.). If the operation state of the internal combustion engine is changed while the control for raising the temperature of the exhaust gas purification device to the target temperature is performed, the temperature of the exhaust gas flowing into the front catalyst and the flow rate of the exhaust gas flowing into the front catalyst change. In addition, the temperature of the exhaust purification device may also change.

  As a result, even if the temperature of the upstream catalyst is raised to the temperature set when the temperature raising control of the exhaust gas purification device is performed (the temperature that can be raised later), the temperature of the exhaust gas purification device is reliably raised to the target temperature thereafter. There is a possibility that it cannot be made. For example, a case where the operating state of the internal combustion engine is changed to an idle state, a low load, or the like after the temperature raising control of the exhaust purification device is performed, and the temperature of the exhaust gas flowing out from the internal combustion engine excessively decreases can be exemplified.

Therefore, the present invention for raising the temperature of the exhaust purification device to the target temperature more reliably,
After the pre-stage catalyst has been heated up to the post-stage temperature rise temperature, the supply heat quantity that is the heat quantity that is supplied from the pre-stage catalyst to the exhaust purification device by causing the exhaust flow rate changing means to execute the catalyst side increase control is obtained. The apparatus may further include a determination unit that determines whether the amount of heat necessary for raising the temperature of the exhaust gas purification device to the target temperature is less than a necessary amount of heat.

  Here, the determination means is configured to discharge exhaust from the front stage catalyst at the rear stage temperature rise possible temperature based on the temperature of the exhaust gas flowing into the front stage catalyst, the flow rate of the exhaust gas flowing into the front stage catalyst, and the temperature of the front stage catalyst (temperature that can be raised at the rear stage). The amount of heat that can be supplied to the exhaust gas purification device (the amount of heat supplied) may be calculated. Further, based on the temperature of the exhaust purification device, the target temperature of the exhaust purification device, and the flow rate of the exhaust gas flowing into the exhaust purification device, the amount of heat (necessary heat amount) required to raise the temperature of the exhaust purification device to the target temperature is calculated. It may be calculated.

  Then, when the determination means determines that the supplied heat quantity is less than the necessary heat quantity, the exhaust flow rate changing means is caused to execute the catalyst side increase control, and the reducing agent supply means supplies the reducing agent to the preceding stage. The exhaust gas purification device may be heated to the target temperature by being supplied to the catalyst and the exhaust gas purification device.

  Thereby, it is possible to suppress the temperature of the pre-stage catalyst from which heat is removed by the exhaust gas from being excessively low, and to maintain the pre-stage catalyst at a high temperature. That is, when the supplied heat amount can be insufficient with respect to the required heat amount, the supplied heat amount can be supplemented. Therefore, the exhaust purification device can be reliably heated to the target temperature.

  In the present invention, the exhaust gas purification device has a filter capable of collecting particulate matter (PM) in the exhaust gas, and the reducing agent supply means supplies the reducing agent to the filter by supplying the reducing agent to the filter. PM regeneration control execution means for executing PM regeneration control for oxidizing and removing the collected particulate matter (PM) may be further provided.

  Thus, according to the exhaust gas purification system having the above-described configuration, the temperature of the filter can be quickly raised to a temperature at which PM can be oxidized (combusted), and PM regeneration control can be suitably executed.

  Further, usually, the PM regeneration control is often continued for a relatively long period (for example, several minutes). In that case, even if the temperature of the filter is once increased to the target temperature, the temperature of the filter is excessively lower than the target temperature during execution of the PM regeneration control, and the PM trapped in the filter is suitably oxidized and removed. You may not be able to.

  Therefore, in the present invention, when the PM regeneration control executing means executes the PM regeneration control, the exhaust flow rate changing means may execute the catalyst side increase control. In other words, the bypass side flow rate may be decreased, the catalyst side flow rate may be increased, and the reducing agent may be supplied to the filter by the reducing agent supply means.

  Thereby, the temperature of the filter can be maintained at the target temperature (a temperature at which PM can be oxidized) during execution of PM regeneration control. That is, PM can be suitably oxidized and removed over a period during which PM regeneration control is executed.

  Further, since the catalyst side flow rate is increased when PM regeneration control is executed, oxygen contained in the exhaust can always be supplied to the filter. Thereby, it becomes possible to oxidize and remove PM collected by the filter more suitably.

  In the present invention, the exhaust purification device has a NOx catalyst capable of reducing NOx in the exhaust gas, and the NOx catalyst includes the NOx catalyst by causing the reducing agent supply means to supply the reducing agent to the NOx catalyst. A performance regeneration control executing means for executing NOx reduction control for reducing the NOx and / or SOx poisoning recovery control for recovering SOx poisoning of the NOx catalyst may be further provided.

  Here, when the performance regeneration control execution means in the present invention executes NOx reduction control or SOx poisoning recovery control, the control of the exhaust flow rate changing means may be made different depending on the type of NOx catalyst.

  For example, when the NOx catalyst in the present invention is an NOx storage reduction catalyst, the exhaust gas purification apparatus is used over a period in which performance regeneration control (NOx reduction control, SOx poisoning recovery control, etc.) is performed by the performance regeneration control execution means. If the flow rate of the exhaust gas passing through the catalyst is reduced, the efficiency of the performance regeneration control for the NOx catalyst is improved, which is more preferable.

  Therefore, in the present invention when the exhaust purification device has an NOx storage reduction catalyst, the bypass passage includes a portion upstream of the reducing agent addition means in the exhaust passage and a downstream portion of the exhaust purification device. The exhaust gas passing through the exhaust passage may be bypassed by the upstream oxidation catalyst and the exhaust purification device.

  And when making the said performance regeneration control execution means perform the said NOx reduction | restoration control and / or the said SOx poisoning recovery | restoration control, you may make it make the said exhaust flow volume change means perform the said catalyst side reduction | decrease control. That is, the reducing agent may be supplied to the NOx storage reduction catalyst by the reducing agent supply means in a state where the bypass side flow rate is increased and the catalyst side flow rate is decreased.

  Thereby, since the exhaust gas passing through the bypass passage bypasses the upstream catalyst and the exhaust gas purification device, the flow rate of the exhaust gas passing through the exhaust gas purification device can be reduced by increasing the bypass flow rate. As a result, it is possible to prevent the reducing agent supplied to the NOx storage reduction catalyst from remaining on the NOx catalyst and slipping downstream of the NOx catalyst.

  That is, according to the present invention, the NOx reduction efficiency in the NOx storage reduction catalyst when the NOx reduction control is executed, and the SOx reduction efficiency in the NOx storage reduction catalyst when the SOx poisoning recovery control is executed are as follows. Thus, the amount of the reducing agent supplied to the NOx catalyst can be saved.

  In the present invention, the reducing agent supplied from the reducing agent supply means first passes through the pre-stage catalyst before flowing into the exhaust purification device. Thereby, the dispersing effect is improved by reducing the molecular weight of the reducing agent, and a so-called reducing agent modification effect can be obtained. As a result, the NOx reduction efficiency and the SOx reduction efficiency described above can be further improved, and the amount of the reducing agent supplied by the reducing agent supply means can be more suitably saved.

  For example, when the NOx catalyst in the present invention is a selective reduction type NOx catalyst, the flow rate of exhaust gas passing through the exhaust purification device may be increased when NOx is reduced in the selective reduction type NOx catalyst. That is, since the selective reduction type NOx catalyst reduces NOx flowing into the selective reduction type NOx catalyst in a reducing atmosphere, the efficiency of the NOx reduction control is improved by increasing the flow rate of the exhaust gas passing through the exhaust purification device. Because.

  Note that the target temperature for raising the temperature of the exhaust purification device (NOx catalyst) is set to a different temperature when the NOx reduction control is executed for the NOx catalyst and when the SOx poisoning recovery control is executed. Of course it is good.

  For example, the target temperature of the exhaust gas purification device (NOx catalyst) when the performance regeneration control execution unit executes NOx reduction control may be the activation temperature of the NOx catalyst. This is because when the NOx catalyst is not active, the NOx purification rate in the NOx catalyst is significantly reduced even if the reducing agent is supplied by the reducing agent supply means.

  Further, the target temperature of the exhaust purification device (NOx catalyst) when the performance regeneration control execution means executes SOx poisoning recovery control may be a temperature at which SOx can be reduced from the NOx catalyst (for example, 600 ° C. to 650 ° C.). good.

  Further, when the NOx catalyst in the present invention is an NOx storage reduction catalyst, fuel or the like as a reducing agent may be supplied by a reducing agent supply means. When the NOx catalyst is a selective reduction type NOx catalyst, urea water or ammonia water as a reducing agent may be supplied by the reducing agent supply means.

  In the present invention, the former stage catalyst activation means may be further provided. When the temperature of the front stage catalyst is lower than the activation temperature of the front stage catalyst, the front stage catalyst activation means may raise the temperature of the front stage catalyst to the activation temperature.

  The above-mentioned pre-catalyst activation means may have, for example, a glow plug or an electric heater. Then, the temperature of the upstream catalyst may be raised by a glow plug, an electric heater, or the like. Further, the electric heater may be provided on the upstream side of the upstream catalyst in the exhaust passage, or may be configured integrally with the upstream catalyst. Further, when the pre-stage catalyst is an electrically heated catalyst, the temperature of the pre-stage catalyst may be raised by energizing the electrically heated catalyst.

  Further, even if a special heating device such as the above glow plug or electric heater is not used, the pre-catalyst activation means increases the fuel injection amount of the internal combustion engine and the temperature of the exhaust gas discharged from the internal combustion engine. The pre-catalyst may be heated up to the activation temperature by raising.

  In the present invention, the exhaust gas purification device provided in the exhaust passage of the internal combustion engine can be quickly raised to the target temperature required for the exhaust gas purification device.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its intake / exhaust system and control system in this embodiment. In FIG. 1, an intake pipe 2 through which intake air flowing into the internal combustion engine 1 flows is connected to the internal combustion engine 1. The intake pipe 2 adjusts the flow rate of intake air flowing through the intake pipe 2. A throttle valve 3 is provided. An air flow meter 4 that outputs an electrical signal corresponding to the amount of intake air flowing through the intake pipe 2 is attached to the intake pipe 2 upstream of the throttle valve 3.

Further, an exhaust pipe 5 through which exhaust from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). In the middle of the exhaust pipe 5,
An exhaust gas purification device 10 for purifying exhaust gas is disposed. In the exhaust purification device 10, a filter 10a that collects particulate matter (hereinafter simply referred to as "PM") in the exhaust, and a NOx storage reduction catalyst (hereinafter simply referred to as "NOx catalyst") that purifies NOx in the exhaust. 10b is also arranged. Hereinafter, in the exhaust pipe 5, the upstream side of the exhaust purification device 10 is referred to as a first exhaust pipe 5 a and the downstream side is referred to as a second exhaust pipe 5 b. Here, in the present embodiment, the first exhaust pipe 5a and the second exhaust pipe 5b correspond to the exhaust passage in the present invention.

  The first exhaust pipe 5a is provided with an oxidation catalyst 11 having a smaller diameter (small cross-sectional area) than that of the first exhaust pipe 5a. A fuel addition valve 12 for adding fuel as an agent is provided. This fuel addition valve 12 is provided close to the upstream of the oxidation catalyst 11. The fuel added from the fuel addition valve 12 is supplied to the oxidation catalyst 11 by the fuel pressure of the fuel addition valve 12 regardless of the flow rate of the exhaust gas passing through the oxidation catalyst 12. Here, in this embodiment, the fuel addition valve 12 corresponds to the reducing agent supply means in the present invention. In the present embodiment, the oxidation catalyst 11 corresponds to the former stage catalyst in the present invention.

  Further, a portion of the first exhaust pipe 5a on the upstream side of the fuel addition valve 12 and the second exhaust pipe 5b are communicated with each other by a bypass pipe 5c. That is, in the present embodiment, the oxidation catalyst 11 and the exhaust purification device 10 can be bypassed to the exhaust gas by passing the bypass pipe 5c through the exhaust gas. Here, in this embodiment, the bypass pipe 5c corresponds to the bypass passage in the present invention.

  The first exhaust pipe 5a communicates with the bypass pipe 5c with an exhaust switching valve 20 that can switch between exhaust gas passing through the oxidation catalyst 11 and the bypass pipe 5c. Yes. Here, the stop position of the exhaust gas switching valve 20 when the exhaust gas passes through the oxidation catalyst 11 side is the “catalyst side position”, and the stop position of the exhaust gas switch valve 20 when the exhaust gas passes through the bypass pipe 5c side is the “bypass side position”. Called.

  A glow plug 13 that generates heat when energized is provided immediately upstream of the oxidation catalyst 11 in the first exhaust pipe 5a. A first temperature sensor 14 for detecting the temperature of the exhaust gas flowing into the oxidation catalyst 11 is provided upstream of the oxidation catalyst 11 in the first exhaust pipe 5a. Further, a second temperature sensor 15 for detecting the temperature of the oxidation catalyst 11 is provided in a portion between the oxidation catalyst 11 and the exhaust purification device 10 in the first exhaust pipe 5a, and an exhaust purification device 10 is provided in the second exhaust pipe 5b. A third temperature sensor 16 for detecting temperature is provided.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 30 for controlling the internal combustion engine 1 and the intake / exhaust system. The ECU 30 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 driver's request, and performs control related to the fuel addition valve 12 and the exhaust switching valve 20 of the internal combustion engine 1. It is.

  The ECU 30 includes sensors for controlling the operating state of the internal combustion engine 1 such as a crank position sensor 7 for detecting the rotational speed of the internal combustion engine 1, an accelerator position sensor 8 for detecting the accelerator opening, and an air flow meter 4. The first temperature sensor 14 to the third temperature sensor 16 are connected via electrical wiring, and their output signals are input to the ECU 30. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1, a fuel addition valve 12, a glow plug 13, and an exhaust switching valve 20 are connected to the ECU 30 via electrical wiring, and are controlled by the ECU 30. It has become.

The ECU 30 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data.

<Temperature control>
Next, control for increasing the temperature of the exhaust purification device 10 to the target temperature required for the exhaust purification device 10 in the exhaust purification system of the present embodiment will be described. Here, temperature rising control for increasing the temperature TF of the filter 10a to the filter target temperature TFt will be described as an example. The filter target temperature TFt is a target temperature required for the filter 10a, and corresponds to the target temperature required for the exhaust emission control device in the present invention. In this embodiment, first, fuel is added from the fuel addition valve 12 with the stop position of the exhaust gas switching valve 20 set to the bypass side position, and the temperature of the oxidation catalyst 11 is increased to the oxidation catalyst target temperature TOt. A fuel addition valve 12 for adding fuel as a reducing agent to the exhaust gas is provided on the upstream side of the oxidation catalyst 11. The exhaust addition valve 12 is provided close to the upstream of the oxidation catalyst 11. Therefore, the fuel added from the exhaust addition valve 12 efficiently passes through the oxidation catalyst 11.

  Here, the oxidation catalyst target temperature TOt is the target temperature of the oxidation catalyst that is required to raise the temperature of the filter 10a to the filter target temperature TFt by flowing exhaust gas that passes through the oxidation catalyst 11 and becomes high temperature into the filter 10a. is there. This oxidation catalyst target temperature TOt is a temperature experimentally obtained in advance, and may be a temperature higher than the filter target temperature TFt. In this embodiment, the oxidation catalyst target temperature TOt corresponds to the temperature that can be raised at the rear stage in the present invention.

  Further, as described above, since the diameter of the oxidation catalyst 11 is smaller than that of the first exhaust pipe 5a, the heat capacity of the oxidation catalyst 11 can be reduced as compared with the case where the diameter is the same as the diameter of the first exhaust pipe 5a. it can. Further, when the diameter of the oxidation catalyst 11 is small, the flow resistance of the exhaust gas flowing into the oxidation catalyst 11 is larger than when the oxidation catalyst 11 is large, so that the oxidation reaction of the fuel can be promoted in the oxidation catalyst 11. Thereby, the temperature TO of the oxidation catalyst 11 can be increased more quickly to the oxidation catalyst target temperature TOt.

  Then, after the oxidation catalyst 11 is heated to the oxidation catalyst target temperature TOt, the fuel addition by the fuel addition valve 12 is stopped, and the stop position of the exhaust gas switching valve 20 is changed to the catalyst side position. Then, the flow rate of the exhaust gas that passes through the oxidation catalyst 11 and the filter 10a increases rapidly. Here, since the oxidation catalyst 11 in this embodiment has a small heat capacity as described above, it can efficiently supply heat to the exhaust gas. Then, the temperature rises when passing through the oxidation catalyst 11, and the exhaust gas that has reached a high temperature flows into the downstream filter 10a, whereby the temperature of the filter 10a rises. Thereby, the temperature of the filter 10a can be rapidly raised to the filter target temperature TFt. Here, in this embodiment, the ECU 30 that changes the stop position of the exhaust gas switching valve 20 corresponds to the exhaust gas flow rate changing means in the present invention.

  Here, FIG. 2 is a flowchart showing a temperature raising control routine in the present embodiment. This routine is a program stored in the ROM in the ECU 30, and is executed every time there is a temperature increase request for the filter 10a. Further, when this routine is executed, description will be made on the assumption that the stop position of the exhaust gas switching valve 20 is the catalyst side position.

  First, in step S101, the ECU 30 estimates the temperature TO of the oxidation catalyst 11, and determines whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the activation temperature TOa (for example, 200 ° C. to 250 ° C.). That is, in this step, it is determined whether or not the fuel added from the fuel addition valve 12 can be oxidized in the oxidation catalyst 11. Further, the temperature TO of the oxidation catalyst 11 is estimated from the detection value of the second temperature sensor 15.

  And when it determines with temperature TO of the oxidation catalyst 11 being lower than the activation temperature TOa, it progresses to step S102. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is equal to or higher than the activation temperature TOa, the process proceeds to step S105.

  In step S102, the glow plug 13 is energized by a command from the ECU 30. As a result, the glow plug 13 generates heat, and the temperature of the exhaust gas flowing into the oxidation catalyst 11 rises. In this step, since the stop position of the exhaust gas switching valve 20 is the catalyst side position, the heat generated in the glow plug 13 can be suitably transmitted to the oxidation catalyst 11. Then, when step S102 is completed, the process proceeds to step S103.

  In step S103, the temperature TO of the oxidation catalyst 11 is estimated, and it is determined whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the activation temperature TOa. And when it determines with temperature TO of the oxidation catalyst 11 being more than the activation temperature TOa, it progresses to step S104. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is lower than the activation temperature TOa, the process returns to step S102. That is, energization to the glow plug 13 is continued.

  Next, in step 104, energization to the glow plug 13 is stopped by a command from the ECU 30. Then, when the process of step S104 ends, the process proceeds to step S105.

  In step S105, the stop position of the exhaust gas switching valve 20 is changed to a bypass side position by a command from the ECU 30. If it does so, almost all the exhaust_gas | exhaustion discharged | emitted from the internal combustion engine 1 will pass the bypass pipe 5c, and the flow volume of the exhaust_gas | exhaustion which passes the oxidation catalyst 11 will become substantially zero. Here, in the present embodiment, the control in which the ECU 30 changes the stop position of the exhaust gas switching valve 20 to the bypass side position corresponds to the catalyst side reduction control in the present invention.

  In subsequent step S106, fuel addition by the fuel addition valve 12 is started. Then, the temperature of the oxidation catalyst 11 is raised by adding fuel directly to the oxidation catalyst 11 from the fuel addition valve 12 provided immediately upstream of the oxidation catalyst 11. Here, by setting the flow rate of the exhaust gas passing through the oxidation catalyst 11 to be substantially zero, it is possible to suppress the removal of heat, fuel, and the like due to the exhaust gas, and to more suitably increase the temperature TO of the oxidation catalyst 11. Then, when the process of step S106 ends, the process proceeds to step S107.

  In step S107, the temperature TO of the oxidation catalyst 11 is estimated from the detection value of the second temperature sensor 15, and it is determined whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the oxidation catalyst target temperature TOt. And when it determines with temperature TO of the oxidation catalyst 11 being more than the oxidation catalyst target temperature TOt, it progresses to step S108. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is lower than the oxidation catalyst target temperature TOt, the process returns to step S106. That is, the fuel addition by the fuel addition valve 12 is continued, and the temperature increase control of the oxidation catalyst 11 is continued.

  In step S108, the fuel addition by the fuel addition valve 12 is stopped by a command from the ECU 30. In subsequent step S109, the ECU 30 changes the stop position of the exhaust gas switching valve 20 to the catalyst side position. As a result, almost all of the exhaust discharged from the internal combustion engine 1 passes through the oxidation catalyst 11 and the filter 10a, and the flow rate of the exhaust passing through the bypass pipe 5c becomes substantially zero. Here, in this embodiment, the control in which the ECU 30 changes the stop position of the exhaust gas switching valve 20 to the catalyst side position corresponds to the catalyst side increase control in the present invention. Then, when the process of step S108 ends, the process proceeds to step S109.

In the subsequent step S110, the temperature of the exhaust gas flowing into the oxidation catalyst 11 from the detection value of the first temperature sensor 14 by the ECU 30 (hereinafter simply referred to as “entered gas temperature”) TE is oxidized from the detection value of the air flow meter 4. A flow rate of exhaust gas flowing into the catalyst 11 (hereinafter, simply referred to as “entry gas amount”) VE is estimated. Then, when the process of step S110 ends, the process proceeds to step S111.

  In step S111, whether or not the supply heat quantity QS, which is the heat quantity supplied from the oxidation catalyst 11 to the filter 10a by the ECU 30, is less than the necessary heat quantity QN, which is the heat quantity required to raise the temperature of the filter 10a to the filter target temperature TFt. Determined. That is, in this step, it is determined whether it is difficult to raise the temperature TF of the filter 10a to the filter target temperature TFt without restarting the fuel addition valve 12 from adding fuel. Here, in the present embodiment, the ECU 30 that determines whether or not the supplied heat quantity QS is less than the necessary heat quantity QN corresponds to the determination means in the present invention.

  Specifically, the supply heat quantity QS is calculated based on the incoming gas temperature TE, the incoming gas quantity VE, and the oxidation catalyst target temperature TOt. For example, you may derive | lead-out by reading supply heat quantity QS from the map in which the relationship between the said parameter and supply heat quantity QS was stored.

  Further, the necessary heat quantity QN is calculated based on the temperature TF of the filter 10a, the filter target temperature TFt, and the amount of entering gas VE. For example, you may derive | lead-out by reading the required heat quantity QN from the map in which the relationship between the said parameter and the required heat quantity QN was stored. The temperature TF of the filter 10a is estimated from the detection value of the third temperature sensor 16.

  When the ECU 30 determines that the supplied heat quantity QS is less than the required heat quantity QN, the process proceeds to step S112. On the other hand, when it is determined that the supplied heat quantity QS is equal to or higher than the necessary heat quantity QN, it is determined that the temperature TF of the filter 10a can be raised to the filter target temperature TFt, and this routine is temporarily ended.

  In step S112, the addition of fuel by the fuel addition valve 12 is restarted by a command from the ECU 30. Thereby, the fuel reacts in the oxidation catalyst 11, and the reaction heat can be supplied to the filter 10a. Then, when the process of step S112 ends, the process proceeds to step S113.

  In step S113, the ECU 30 estimates the temperature TF of the filter 10a from the detection value of the third temperature sensor 16, and determines whether or not the temperature TF of the filter 10a is equal to or higher than the filter target temperature TFt. That is, in this step, it is determined whether or not the temperature increase control for the filter 10a may be terminated. And when it determines with temperature TF of the filter 10a being lower than filter target temperature TFt, it returns to step S112. That is, the fuel addition by the fuel addition valve 12 is continued. As a result, the temperature TF of the filter 10a increases. On the other hand, if it is determined that the temperature TF of the filter 10a is equal to or higher than the filter target temperature TFt, the process proceeds to step S114.

  In step S114, the fuel addition by the fuel addition valve 12 is stopped by a command from the ECU 30. Then, when the process of step S114 ends, this routine is once ended.

  As described above, according to this routine, the temperature of the filter 10a can be quickly raised to the filter target temperature TFt. If it is determined in step S111 that the supply heat quantity QS is equal to or greater than the necessary heat quantity QN, it is not necessary to restart the fuel addition by the fuel addition valve 12, and the fuel addition quantity can be saved.

Further, according to the temperature increase control according to the present embodiment, it can be suitably determined whether or not to add fuel supplementarily based on the supplied heat quantity QS and the required heat quantity QN. Therefore, for example, even if the operating state of the internal combustion engine 1 is changed during execution of this routine and the input gas temperature TE is excessively lowered, the temperature of the filter 10a can be reliably raised to the filter target temperature TFt.

<PM regeneration control>
Further, when the above temperature increase control routine is applied to the PM regeneration control for oxidizing and removing the PM collected by the filter 10a, the filter target temperature TFt is set to a temperature at which PM can be oxidized (for example, 500 ° C. to 700 ° C. (° C). Then, it is possible to oxidize and remove the PM collected by the filter 10a.

  In addition, since the PM regeneration control is often continued for a relatively long period (for example, several minutes), even if the temperature of the filter 10a is raised to a temperature at which PM can be oxidized, the temperature TF of the filter 10a is subsequently increased. When it falls, there exists a possibility that the oxidation efficiency of PM may fall. Therefore, in the PM regeneration control in the present embodiment, the fuel addition valve 12 may be continuously added after the temperature TF of the filter 10a is raised to the filter target temperature TFt.

  Further, since the PM regeneration control in the present embodiment is executed in a state where the stop position of the exhaust gas switching valve 20 is stopped at the catalyst side position, oxygen necessary for oxidizing the PM collected by the filter 10a is added to the PM regeneration control. It can be made to flow suitably into the filter 10a.

<NOx reduction control>
Next, the NOx reduction control for the NOx catalyst 10b in the present embodiment will be described. FIG. 3 is a flowchart showing the NOx reduction control routine in this embodiment. This routine is a program stored in the ROM in the ECU 30 and is executed at predetermined intervals while the internal combustion engine 1 is in operation.

  When this routine is executed, first, in step S201, it is determined whether or not a NOx reduction request has been issued to the NOx catalyst 10b. Here, the NOx reduction request may be issued, for example, based on the integrated value of the intake air amount after the previous NOx reduction control is completed. Further, a NOx sensor (not shown) may be provided in the second exhaust pipe 5b, and the second exhaust pipe 5b may be output based on the output of the NOx sensor.

  Here, if it is determined that the NOx reduction request has not been issued, the present routine is temporarily terminated as it is. On the other hand, if it is determined that the NOx reduction request has been issued, the process proceeds to step S202. In step S202, the temperature TN of the NOx catalyst 10b is estimated based on the detection value of the third temperature sensor 16, and whether or not the temperature TN of the NOx catalyst 10b is lower than the activation temperature TNa (for example, 200 ° C. to 250 ° C.). Is determined.

  If it is determined that the temperature TN of the NOx catalyst 10b is lower than the activation temperature TNa, it is determined that it is necessary to raise the temperature of the NOx catalyst 10b, and the process proceeds to step S203. On the other hand, if it is determined that the temperature TN of the NOx catalyst 10b is equal to or higher than the activation temperature TNa, the process proceeds to step S204.

In step S203, NOx catalyst temperature increase control for increasing the temperature of the NOx catalyst 10b to the activation temperature TNa is executed. Specifically, the above-described temperature increase control routine (steps S101 to S113) is executed. Here, the terms used in the temperature raising control routine are read as follows. That is, the filter 10a, the temperature TF of the filter 10a, and the filter target temperature TFt are read as the temperature TN of the NOx catalyst 10b, the NOx catalyst 10b, and the NOx catalyst target temperature TNt, respectively. Then, the NOx catalyst target temperature TNt when the above routine is executed may be set as the activation temperature TNa of the NOx catalyst 10b. As a result, when the temperature TN of the NOx catalyst 10b is lower than the activation temperature TNa, the NOx catalyst 10b can be quickly raised to the activation temperature TNa.

  In this routine, the NOx catalyst target temperature TNt corresponds to the target temperature required for the exhaust emission control device according to the present invention. Then, when the process of step S203 ends, the process proceeds to step S204.

  In step S204, the stop position of the exhaust gas switching valve 20 is again changed to the bypass position by a command from the ECU 30. Then, in the subsequent step S205, fuel for reducing NOx stored in the NOx catalyst 10b is added by the fuel addition valve 12 in accordance with a command from the ECU 30. Thereby, the NOx stored in the NOx catalyst 10b is reduced. Then, in the subsequent step S206, the stop position of the exhaust gas switching valve 20 is changed again to the catalyst side position by a command from the ECU 30, and this routine is temporarily ended.

  As described above, according to the NOx reduction control according to this routine, even when the NOx catalyst 10b is not activated, the NOx reduction control can be performed efficiently after being activated quickly. Further, when NOx is reduced in the NOx catalyst 10b, the flow rate of the exhaust gas passing through the NOx catalyst 10b is made substantially zero, so that the fuel added from the fuel addition valve 12 slips downstream from the NOx catalyst 10b. Can be suppressed. That is, the amount of fuel added can be saved and the NOx reduction efficiency can be improved.

<Modification of NOx reduction control>
Next, control for further improving the reduction efficiency of NOx stored in the NOx catalyst 10b will be described. The following control may be performed before the process of step S204 is executed after the process of step S203 of the NOx reduction control routine is completed. That is, it is determined whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the NOx reduction target temperature TOt2.

  Then, when it is determined that the temperature TO of the oxidation catalyst 11 is equal to or higher than the NOx reduction target temperature TOt2, the processes after step S204 are executed. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is lower than the NOx reduction target temperature TOt2, the temperature of the oxidation catalyst 11 is increased until the temperature TO of the oxidation catalyst 11 becomes equal to or higher than the second oxidation catalyst target temperature TOt2. Is done. Thereby, the fuel added from the fuel addition valve 12 is reformed when the temperature TO of the oxidation catalyst 11 is lower than when the temperature TO is low, and the NOx reduction efficiency is improved.

  The second oxidation catalyst target temperature TOt2 is a target temperature required for the oxidation catalyst 11 when NOx is reduced in the NOx catalyst 10b, and may be obtained experimentally in advance. Further, when the temperature of the oxidation catalyst 11 is raised, it is more preferable to add fuel from the fuel addition valve 12 with the exhaust switching valve 20 stopped at the bypass side position. This makes it possible to reduce the slipping of fuel to the downstream side of the NOx catalyst 10b and the removal of heat as much as possible, and raise the oxidation catalyst 11 more quickly to the second oxidation catalyst target temperature TOt2. be able to.

  In this embodiment, the case where the present invention is applied to the NOx reduction control for the NOx storage reduction catalyst has been exemplarily described. However, the present invention is also applied to an exhaust purification system including a selective reduction NOx catalyst. Can be applied. In that case, instead of the fuel addition valve 12, a urea water addition valve for adding urea water as a reducing agent may be provided. Further, ammonia water may be added instead of urea water.

The selective reduction type NOx catalyst is not a NOx catalyst that reduces the stored NOx in the NOx reduction atmosphere, but a NOx catalyst that reduces NOx in the exhaust gas when the exhaust gas passes through the selective reduction type NOx catalyst. It is. Therefore, in order to promote the NOx reduction reaction in the selective reduction type NOx catalyst, the NOx reduction efficiency can be improved by increasing the flow rate of the exhaust gas passing through the selective reduction type NOx catalyst.

  Therefore, when reducing NOx in the selective reduction type NOx catalyst, the stop position of the exhaust gas switching valve 20 may not be changed to the bypass side position in step S204 of the NOx reduction control routine. That is, NOx can be reduced more suitably by making the selective reduction type NOx catalyst into a NOx reducing atmosphere while ensuring the flow rate of the exhaust gas passing through the selective reduction type NOx catalyst.

  Next, an embodiment different from the first embodiment of the exhaust gas purification system for the internal combustion engine 1 according to the present invention will be described. FIG. 4 is a diagram showing a schematic configuration of the internal combustion engine 1 and its intake / exhaust system and control system in the present embodiment. Here, the same or equivalent components as those in the exhaust purification system of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The present embodiment differs from the exhaust purification system according to Embodiment 1 in the following points. That is, the oxidation catalyst 11 in the present embodiment is an electrically heated oxidation catalyst provided with an electric heater 11a that generates heat when energized. In the present embodiment, the glow plug 13 is not provided.

  In this embodiment, a first flow rate change valve 21 and a second flow rate change valve 22 that can change the flow rate of the exhaust gas are provided instead of the exhaust gas switching valve. Here, the first flow rate change valve 21 is provided in the middle part of the exhaust bypass pipe 5c, and the second flow rate change valve 22 is a part of the second exhaust pipe 5b on the upstream side of the connection part with the bypass pipe 5c. Is provided.

  Here, the electric heater 11a, the first flow rate change valve 21, and the second flow rate change valve 22 are connected to the ECU 30 via electric wiring, and are controlled by the ECU 30. In other words, the temperature of the oxidation catalyst 11 can be raised when the ECU 30 energizes the electric heater 11a.

  Further, the ECU 30 can change the flow rate of the exhaust gas passing through the bypass pipe 5c by changing the opening degree DF of the first flow rate changing valve 21. Further, the flow rate of the exhaust gas passing through the exhaust purification device 10 can be changed by changing the opening DS of the second flow rate change valve 22.

<SOx poisoning recovery control>
Next, SOx poisoning recovery control for recovering the NOx catalyst 10b poisoned by SOx in the exhaust gas in the exhaust purification system having the above configuration will be described with reference to the flowchart of FIG.

  FIG. 5 is a flowchart showing the SOx poisoning recovery control routine in this embodiment. This routine is a program stored in the ROM in the ECU 30 and is executed at predetermined intervals while the internal combustion engine 1 is in operation. The opening degree of the first flow rate changing valve 21 (hereinafter simply referred to as “first opening degree”) DF is fully closed, and the opening degree of the second flow rate changing valve 22 (hereinafter simply referred to as “second opening degree”). This routine will be described on the assumption that DS is fully open. That is, the description will be made on the assumption that substantially all of the exhaust discharged from the internal combustion engine 1 passes through the exhaust purification device 10 (NOx catalyst 10b).

When this routine is executed, first, in step S301, it is determined whether or not an SOx poisoning recovery request has been issued to the NOx catalyst 10b. Here, the SOx poisoning recovery request may be issued based on, for example, an integrated value of the travel distance of the vehicle since the previous SOx poisoning recovery control was executed.

  Here, if it is determined that the SOx poisoning recovery request has not been issued, the present routine is temporarily terminated. On the other hand, if it is determined that the SOx regeneration processing request has been issued, the process proceeds to S302.

  In step S302, the temperature TN of the NOx catalyst 10b is estimated based on the detection value of the third temperature sensor 16, and the temperature TN of the NOx catalyst 10b is higher than the regeneration NOx catalyst target temperature TNs (for example, 600 ° C. to 650 ° C.). Whether it is low is determined. Here, the regeneration NOx catalyst target temperature TNs is a temperature at which SOx stored in the NOx catalyst 10b can be reduced when the reducing agent is supplied to the NOx catalyst 10b (for example, 600 ° C. to 650 ° C.). The temperature is experimentally obtained in advance.

  When it is determined that the temperature TN of the NOx catalyst 10b is lower than the regeneration NOx catalyst target temperature TNs, it is determined that it is necessary to raise the temperature of the NOx catalyst 10b, and the process proceeds to step S303. On the other hand, when it is determined that the temperature TN of the NOx catalyst 10b is equal to or higher than the regeneration NOx catalyst target temperature TNs, the process proceeds to step S313.

  In step S303, the first opening degree DF is changed to fully open and the second opening degree DS is changed to fully closed by a command from the ECU 30. That is, substantially all of the exhaust discharged from the internal combustion engine 1 bypasses the exhaust purification device 10. In step S304, the ECU 30 estimates the temperature TO of the oxidation catalyst 11, and determines whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the activation temperature TOa. And when it determines with temperature TO of the oxidation catalyst 11 being more than the activation temperature TOa, it progresses to step S308. On the other hand, if it is determined that the temperature TO of the oxidation catalyst 11 is lower than the activation temperature TOa, the process proceeds to step S305.

  In step S305, the electric heater 11a is energized by a command from the ECU 30. Thereby, since the oxidation catalyst 11 generates heat, the temperature TO of the oxidation catalyst 11 rises. In addition, since the second opening DS is changed to fully closed in step S302, it is possible to efficiently raise the temperature of the oxidation catalyst 11. Then, when the process of step S305 ends, the process proceeds to step S306.

  In step S306, the temperature TO of the oxidation catalyst 11 is estimated again, and it is determined whether or not the temperature TO of the oxidation catalyst 11 is equal to or higher than the activation temperature TOa. And when it determines with temperature TO of the oxidation catalyst 11 being more than the activation temperature TOa, it progresses to step S307. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is lower than the activation temperature TOa, the process returns to step S305. That is, energization to the electric heater 11a is continued.

  Next, in step 307, energization to the electric heater 11a is stopped by a command from the ECU 30. In subsequent step S308, the ECU 30 causes the fuel addition valve 12 to add fuel so as to raise the temperature TO of the oxidation catalyst 11 to the regeneration oxidation catalyst target temperature TOs. Here, the regeneration oxidation catalyst target temperature TOs is used to raise the temperature of the NOx catalyst 10b to the regeneration NOx catalyst target temperature TNs by flowing exhaust gas that passes through the oxidation catalyst 11 and becomes high temperature into the NOx catalyst 10b. It means the target temperature of the required oxidation catalyst. The regeneration oxidation catalyst target temperature TOs is a temperature that is experimentally obtained in advance, and may be higher than the regeneration NOx catalyst target temperature TNs. In this routine, the regeneration oxidation target temperature TOs corresponds to the temperature that can be raised at the latter stage in the present invention.

In the subsequent step S309, the temperature TO of the oxidation catalyst 11 is estimated, and the oxidation catalyst 1
It is determined whether the temperature TO of 1 is equal to or higher than the regeneration oxidation target temperature TOs. And when it determines with temperature TO of the oxidation catalyst 11 being more than the oxidation catalyst target temperature TOs at the time of reproduction | regeneration, it progresses to step S310. On the other hand, when it is determined that the temperature TO of the oxidation catalyst 11 is lower than the regeneration oxidation target temperature TOs, the process returns to step S308. That is, fuel is continuously added by the fuel addition valve 12.

  In step S310, the fuel addition by the fuel addition valve 12 is stopped by a command from the ECU 30. In step S311, the first opening degree DF is changed to fully closed and the second opening degree DS is changed to full opening in response to a command from the ECU 30. As a result, the flow rate of the exhaust gas passing through the NOx catalyst 10b increases rapidly. That is, thermal energy is supplied from the oxidation catalyst 11 to the NOx catalyst 10b via the high-temperature exhaust, and the temperature TN of the NOx catalyst 10b can be rapidly increased.

  In subsequent step S312, the ECU 30 estimates the temperature TN of the NOx catalyst 10b, and determines whether or not the temperature TN of the NOx catalyst 10b is equal to or higher than the NOx catalyst target temperature TNs during regeneration. When it is determined that the temperature TN of the NOx catalyst 10b is lower than the regeneration NOx catalyst target temperature TNs, the process returns to step S311. That is, thermal energy is supplied from the oxidation catalyst 11 to the NOx catalyst 10b through the high-temperature exhaust gas until the temperature TN of the NOx catalyst 10b becomes equal to or higher than the regeneration NOx catalyst target temperature TNs. On the other hand, when it is determined that the temperature TN of the NOx catalyst 10b is equal to or higher than the regeneration NOx catalyst target temperature TNs, the process proceeds to step S313.

  In step S313, the first opening degree DF is changed to fully open and the second opening degree DS is changed to fully closed by a command from the ECU 30. As a result, the flow rate of the exhaust gas passing through the NOx catalyst 10b becomes substantially zero. In subsequent step S314, fuel is added to the fuel addition valve 12 in order to reduce the SOx stored in the NOx catalyst 10b. Here, as described above, when the temperature TN of the NOx catalyst 10b is equal to or higher than the regeneration NOx catalyst target temperature TNs, and fuel as a reducing agent is supplied to the NOx catalyst 10b, the NOx catalyst 10b is preferably occluded. The SOx that has been reduced is reduced.

  Further, since the reduction reaction of SOx in the NOx catalyst 10b is performed in a state where the flow rate of the exhaust gas passing through the NOx catalyst 10b is substantially zero, the slipping of fuel from the NOx catalyst 10b and the removal of heat are suppressed, and the SOx. The reduction efficiency of can be improved. In the subsequent step S315, the first opening degree DF is changed to fully closed and the second opening degree DS is changed to fully open in accordance with a command from the ECU 30, and this routine is temporarily ended.

  As described above, according to this routine, the temperature TN of the NOx catalyst 10b can be quickly raised to the regeneration NOx catalyst target temperature TNs necessary for executing the SOx poisoning recovery control. The SOx poisoning recovery control can be executed.

  In the routine described above, the control for changing the first opening DF and the second opening DS to either fully open or fully closed has been described. However, the present invention is not limited to this. For example, “a predetermined opening on the opening side” may be used instead of “fully open”, or “a predetermined opening on the closing side” may be used instead of “fully closed”.

In the above-described embodiment, when the oxidation catalyst 11 is not activated, the temperature TO of the oxidation catalyst 11 is set to the activation temperature TOa by energizing the glow plug 13 (Example 1) and the electric heater 11b (Example 2). However, the present invention is not limited to this. For example, the oxidation catalyst 11 may be heated to the activation temperature TOa by increasing the fuel injection amount of the internal combustion engine 1 and increasing the temperature of the exhaust gas discharged from the internal combustion engine 1.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system and a control system thereof in Embodiment 1. FIG. 3 is a flowchart illustrating a temperature increase control routine in the first embodiment. 3 is a flowchart showing a NOx reduction control routine in Embodiment 1. It is a figure which shows schematic structure of the internal combustion engine in Example 2, its intake-exhaust system, and a control system. 7 is a flowchart showing a SOx poisoning recovery control routine in Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake pipe 3 ... Throttle valve 4 ... Air flow meter 5 ... Exhaust pipe 5a ... First exhaust pipe 5b ... Second exhaust pipe 5c ... Bypass pipe 7 ... Crank position sensor 8 ... Accelerator position sensor 10 ... Exhaust gas purification device 10a / Filter 10b / Occlusion reduction type NOx catalyst 11 / Oxidation catalyst 11a / Electric heater 12 / Fuel addition valve 13 / Glow plug 14 First temperature sensor 15 Second temperature sensor 16 Third temperature sensor 20 Exhaust switching valve 21 First flow rate change valve 22 Second flow rate change valve 30 ECU

Claims (3)

An exhaust passage having one end connected to the internal combustion engine and through which the exhaust from the internal combustion engine passes;
A pre-stage catalyst provided in the exhaust passage and having an oxidation function;
An exhaust purification device that is provided downstream of the preceding catalyst in the exhaust passage and purifies exhaust;
A reducing agent supply means that is provided upstream of the preceding catalyst and supplies a reducing agent to the preceding catalyst and the exhaust purification device;
A bypass passage for communicating the upstream portion of the exhaust passage with respect to the reducing agent supply means and the downstream portion of the upstream catalyst, and bypassing the upstream catalyst to the exhaust gas passing through the exhaust passage;
Catalyst side reduction control for increasing the bypass side flow rate, which is the flow rate of the exhaust gas passing through the bypass passage, and decreasing the catalyst side flow rate, which is the flow rate of the exhaust gas passing through the preceding catalyst, and reducing the bypass side flow rate And an exhaust flow rate changing means capable of performing catalyst side increase control for increasing the catalyst side flow rate,
With
When raising the temperature of the exhaust gas purification device to a target temperature required for the exhaust gas purification device, causing the exhaust gas flow rate changing means to execute the catalyst side reduction control and causing the reducing agent supply means to supply the reducing agent. The exhaust gas purification system for an internal combustion engine, wherein the exhaust gas flow rate changing means is caused to execute the catalyst side increase control after raising the temperature of the preceding catalyst to a predetermined temperature that can be raised at the subsequent stage.   The exhaust flow rate changing means makes the flow rate on the catalyst side substantially zero until the temperature of the front catalyst rises to the temperature that can be raised at the rear stage in the catalyst side reduction control, and the front stage catalyst in the catalyst side increase control 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the flow rate on the bypass side is made substantially zero after the temperature is raised to the temperature capable of raising the rear stage. After the pre-stage catalyst has been heated up to the post-stage temperature rise temperature, the supply heat quantity that is the heat quantity that is supplied from the pre-stage catalyst to the exhaust purification device by causing the exhaust flow rate changing means to execute the catalyst side increase control is obtained. A determination means for determining whether or not the exhaust purification device is less than a necessary heat amount that is a heat amount necessary for raising the temperature to the target temperature;
When the determination means determines that the supply heat quantity is less than the required heat quantity, the exhaust flow rate change means performs the catalyst side increase control, and the reducing agent supply means supplies the reducing agent to the pre-stage catalyst and The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein the exhaust purification device is heated to the target temperature by being supplied to the exhaust purification device.

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