JP4155256B2 - 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, and more particularly to an exhaust gas purification system for an internal combustion engine provided with a particulate filter that is provided in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas.

A filter in which filter regeneration control is being executed when an exhaust passage of the internal combustion engine is provided with a particulate filter (hereinafter simply referred to as a filter) that collects particulate matter (hereinafter referred to as PM) in the exhaust gas There is known a technique for increasing the flow rate of exhaust gas flowing into a filter (hereinafter simply referred to as exhaust gas flow rate) when the temperature rise rate of the gas reaches a specified value or more (see, for example, Patent Document 1).
JP 2004-68804 A JP 2002-38930 A Japanese Examined Patent Publication No. 6-21552

  In an exhaust gas purification system for an internal combustion engine provided with a filter provided in an exhaust passage of the internal combustion engine, when the amount of PM deposited on the filter (hereinafter referred to as PM deposition amount) is equal to or greater than a specified PM deposition amount, By raising the temperature of the filter to the target temperature, filter regeneration control for oxidizing and removing PM accumulated on the filter is performed.

  When the engine speed of the internal combustion engine decreases during the execution of such filter regeneration control, the amount of heat taken away from the filter decreases due to a decrease in the exhaust flow rate, and therefore the temperature of the filter rapidly increases. There is. As a result, the temperature of the filter rises to a temperature at which the filter is melted or excessively deteriorated, that is, the filter may be overheated.

  The present invention has been made in view of the above problems, and in an exhaust gas purification system for an internal combustion engine including a filter provided in an exhaust passage of the internal combustion engine, the temperature of the filter is excessively increased during execution of filter regeneration control. It is an object to provide a technique that can be suppressed.

  The present invention assumes that when the filter regeneration control is executed and the temperature of the filter is rising, the engine speed of the internal combustion engine is equal to or lower than the specified engine speed, and the temperature reached by the filter in that case is predicted. . Then, the rate of temperature increase when the temperature of the filter is rising is controlled so that the predicted temperature reached by the filter falls within the allowable range.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
Filter regeneration control execution means for performing filter regeneration control for oxidizing and removing particulate matter deposited on the particulate filter by raising the temperature of the particulate filter to a target temperature;
PM deposition amount detection means for detecting the amount of particulate matter deposited on the particulate filter;
A temperature increase rate detecting means for detecting a temperature increase rate when the filter regeneration control is executed by the filter regeneration control executing means and the temperature of the particulate filter is rising;
When the filter regeneration control is executed by the filter regeneration control execution means and the temperature of the particulate filter is rising, the amount of particulate matter detected by the PM deposition amount detection means and the temperature increase rate detection means An arrival temperature predicting means for predicting an arrival temperature of the particulate filter when the engine speed of the internal combustion engine becomes equal to or less than a specified engine speed based on the detected temperature rise rate;
The temperature increase rate when the filter regeneration control is executed by the filter regeneration control executing means and the temperature of the particulate filter is rising is the allowable upper limit of the temperature reached by the particulate filter predicted by the reached temperature predicting means. A temperature increase rate control means for controlling the temperature to be equal to or lower than the temperature;
It is characterized by providing.

  In the present invention, the filter regeneration control is executed by raising the temperature of the filter to the target temperature. Here, the target temperature is a temperature at which PM accumulated on the filter can be oxidized and removed, and a temperature at which the filter can be prevented from being melted or excessively deteriorated.

  When execution of filter regeneration control is started, the temperature of the filter starts to rise. In the present invention, the temperature rise rate of the filter at this time is detected by the temperature rise rate detecting means. The temperature increase rate is the amount of temperature increase per unit time. Hereinafter, the temperature increase rate of the filter at this time is simply referred to as a filter temperature increase rate.

  When filter regeneration control is executed and the temperature of the filter is rising, if the engine speed of the internal combustion engine decreases, the amount of heat taken away from the filter decreases due to a decrease in the exhaust flow rate, so the filter temperature rises rapidly. May progress. Therefore, at this time, if the engine speed of the internal combustion engine decreases excessively, the temperature of the filter rises above the target temperature, and the filter may eventually overheat.

  At this time, the reached temperature of the filter reached by the rapid increase in the temperature of the filter becomes higher as the PM accumulation amount at the time when the engine speed of the internal combustion engine decreases, and the engine speed of the internal combustion engine increases. The higher the filter temperature increase rate at the time when the number decreases, the higher the value. This is because as the PM deposition amount increases and the filter temperature increase rate increases, PM oxidation is more easily promoted when the engine speed of the internal combustion engine is reduced.

  Therefore, in the present invention, when the filter regeneration control is executed and the temperature of the filter is increasing, the reached temperature of the filter when the engine speed of the internal combustion engine becomes equal to or lower than the specified engine speed is determined at that time. Predicted based on PM deposition amount and filter temperature rise rate. That is, when filter regeneration control is executed and the temperature of the filter is rising, it is assumed that the engine speed of the internal combustion engine has become equal to or lower than the specified engine speed, and the temperature reached by the filter in that case is predicted. Hereinafter, the temperature reached by the filter in this case is simply referred to as the filter temperature.

  Here, if the engine speed of the internal combustion engine becomes equal to or lower than the specified engine speed when the filter regeneration control is executed and the temperature of the filter is rising, the filter may overheat. It is good also as a threshold value of the engine speed which can be judged that there exists. Further, it may be a threshold value of the engine speed at which it can be determined that the operation state of the internal combustion engine is the idle operation.

  Then, the filter temperature increase rate when the filter temperature is rising is controlled so that the predicted filter reaching temperature is equal to or lower than the allowable upper limit temperature. Here, the allowable upper limit temperature is an upper limit value of an allowable temperature determined in advance by an experiment or the like, and is equal to or higher than the target temperature in the filter regeneration control, and suppresses filter melting and excessive deterioration. The temperature is below the upper limit of the possible temperature.

  According to the present invention, even when the engine regeneration speed of the internal combustion engine decreases when the filter regeneration control is executed and the filter temperature is rising, the temperature of the filter can be suppressed to the allowable upper limit temperature or less. . Therefore, it is possible to suppress the temperature of the filter from excessively increasing when the filter regeneration control is executed.

  In the present invention, the rate of increase in the temperature of the filter may be controlled only when the filter regeneration control is executed and the temperature of the filter is rising and when the temperature of the filter is equal to or higher than the specified temperature.

  Even when the filter regeneration control is executed and the temperature of the filter has risen, if the temperature of the filter has not reached a certain level, the engine speed of the internal combustion engine 1 drops below the specified engine speed. As a result, the filter may not overheat.

  Therefore, even when the filter regeneration control is executed and the temperature of the filter is rising, even if the engine speed of the internal combustion engine falls below the specified engine speed, it is possible to determine that the filter is unlikely to overheat. Let the temperature be the specified temperature. This specified temperature is lower than the target temperature.

  According to the control as described above, even when the execution of the filter regeneration control is started, the rate of temperature increase of the filter is not limited while the temperature of the filter is lower than the specified temperature. As a result, the filter temperature can be raised to the target temperature at an earlier time while suppressing the excessive temperature rise of the filter after the start of the execution of the filter regeneration control. Accordingly, the execution time of the filter regeneration control can be shortened as much as possible.

  In the present invention, when the filter temperature increase rate is controlled, the filter increase rate may be controlled to the upper limit value within a range where the filter reached temperature predicted by the reached temperature predicting means is equal to or lower than the allowable upper limit temperature.

  According to such control, it is possible to raise the temperature of the filter to the target temperature at an earlier time while suppressing the excessive temperature rise of the filter after the execution of the filter regeneration control is started. Accordingly, the execution time of the filter regeneration control can be shortened as much as possible.

  According to the exhaust gas purification system for an internal combustion engine according to the present invention, in the exhaust gas purification system for an internal combustion engine provided with a filter provided in the exhaust passage of the internal combustion engine, it is possible to prevent the temperature of the filter from excessively increasing when filter regeneration control is executed. I can do it.

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

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

The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 4 and an exhaust passage 2 are connected to the internal combustion engine 1. A throttle valve 8 is provided in the intake passage 4. On the other hand, the exhaust passage 2 is provided with a particulate filter 3 (hereinafter simply referred to as a filter 3) for collecting PM in the exhaust. Further, the exhaust passage 2 upstream of the filter 3
Is provided with an oxidation catalyst 6. Note that the oxidation catalyst 6 may not be provided in the exhaust passage 2 upstream of the filter 3 but the oxidation catalyst may be supported on the filter 3.

  The exhaust passage 2 is provided with an exhaust differential pressure sensor 9 that outputs an electrical signal corresponding to the differential pressure of exhaust before and after the filter 3 (hereinafter referred to as the differential pressure before and after the filter). An exhaust temperature sensor 7 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust passage 2 is provided in the exhaust passage 2 downstream of the filter 3. A fuel addition valve 5 for adding fuel to the exhaust is provided in the exhaust passage 2 upstream of the filter 3.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. The ECU 10 is electrically connected to an exhaust differential pressure sensor 9, an exhaust temperature sensor 7, a crank position sensor 11 that outputs an electrical signal corresponding to the crank angle of the internal combustion engine 1, and the like, and these output signals are input to the ECU 10. Is done. The ECU 10 estimates the PM accumulation amount in the filter 3 from the output value of the exhaust differential pressure sensor 9, and estimates the temperature of the filter 3 from the output value of the exhaust temperature sensor 7. The ECU 10 is electrically connected to the throttle valve 8 and the fuel addition valve 5, and these are controlled by the ECU 10.

<Filter regeneration control>
In the present embodiment, when PM equal to or greater than the specified PM accumulation amount is accumulated in the filter 3, the ECU 10 reduces the opening of the throttle valve 8 and adds fuel into the exhaust gas from the fuel addition valve 5, thereby filtering the filter. 3 is raised to the target temperature Tt, and filter regeneration control for oxidizing and removing PM deposited on the filter 3 is executed.

  Here, the target temperature Tt is a temperature at which PM deposited on the filter 3 can be oxidized and removed, and a temperature at which the filter 3 can be prevented from being melted or excessively deteriorated. This target temperature Tt is determined in advance by experiments or the like.

  The fuel added from the fuel addition valve 5 is oxidized in the oxidation catalyst 6, and the temperature of the exhaust gas flowing into the filter 3 rises due to the oxidation heat generated at this time. Then, the temperature of the filter 3 increases as the temperature of the exhaust gas increases. Further, the flow rate of the exhaust gas can be reduced by reducing the opening of the throttle valve 8, and as a result, the temperature of the exhaust gas flowing into the filter 3 can be easily increased. Therefore, in this embodiment, the temperature of the filter 3 is adjusted to the target temperature by controlling the amount of fuel added from the fuel addition valve 5 and the opening of the throttle valve 8.

  When the execution of the filter regeneration control is started, the temperature of the filter 3 starts to gradually increase. At this time, when the operating state of the internal combustion engine 1 shifts to the idle operation, the amount of heat taken away from the filter 3 decreases due to the decrease in the exhaust flow rate, and thus the temperature of the filter 3 may increase rapidly. As a result, the temperature of the filter 3 rises above the target temperature Tt, and the filter 3 may eventually overheat.

  At this time, the filter temperature Ta reached when the temperature of the filter 3 rapidly rises increases as the amount of accumulated PM at the time when the operating state of the internal combustion engine 1 shifts to the idle operation increases, and the internal combustion engine 1 The higher the temperature increase rate of the filter at the time when the operation state shifts to the idle operation, the higher it becomes.

<Filter temperature rise rate control>
Therefore, in this embodiment, filter temperature increase rate control is performed to control the filter temperature increase rate Rup when the filter regeneration control is executed and the temperature of the filter 3 is increasing in order to suppress the excessive temperature increase of the filter 3. .

  Here, the control routine of the filter temperature increase rate control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is executed every time the crankshaft rotates by a specified angle during the operation of the internal combustion engine 1.

  In this routine, the ECU 10 first determines in S101 whether or not the filter regeneration control is being executed. When an affirmative determination is made in S101, the ECU 10 proceeds to S102, and when a negative determination is made, the ECU 10 once ends the execution of this routine.

  In S102, the ECU 10 determines whether or not the temperature of the filter 3 is lower than the target temperature Tt. If an affirmative determination is made in S102, it can be determined that the temperature of the filter 3 is rising, so the ECU 10 proceeds to S103. On the other hand, if a negative determination is made in S103, it can be determined that the temperature of the filter 3 has reached the target temperature Tt, that is, the temperature of the filter 3 is not rising, so the ECU 10 executes this routine. Is temporarily terminated.

  In S103, the ECU 10 detects the current PM accumulation amount Qpm.

  Next, the ECU 10 proceeds to S104 and detects the current filter temperature increase rate Rup.

  Next, the ECU 10 proceeds to S105, and calculates the filter reached temperature Ta when the operating state of the internal combustion engine 1 is in the idle operation at the present time based on the PM accumulation amount Qpm and the filter temperature increase rate Rup. Here, the relationship between the PM accumulation amount Qpm, the filter temperature increase rate Rup, and the filter arrival temperature Ta may be obtained in advance by experiments or the like and stored in the ECU 10 as a map.

  Since the temperature of the filter 3 does not reach the target temperature Tt at the present time, the oxidation / removal of PM is hardly performed between the start of the execution of the filter regeneration control and the current time. Therefore, the filter reached temperature Ta may be calculated using the current PM accumulation amount Qpm as the specified PM accumulation amount that becomes the threshold value for starting the filter regeneration control.

  Next, the ECU 10 proceeds to S106, and controls the filter temperature increase rate Rup so that the filter reached temperature Ta becomes equal to or lower than the allowable upper limit temperature Tlimit. Here, the allowable upper limit temperature Tlimit is an upper limit value of an allowable temperature determined in advance by an experiment or the like, and it is possible to suppress melting or frequent deterioration of the filter 3 over the target temperature Tt. The temperature is below the upper limit of the correct temperature.

  Examples of a method for controlling the filter temperature increase rate Rup include a method for adjusting the fuel addition amount from the fuel addition valve 5 and a method for adjusting the exhaust gas flow rate by adjusting the opening of the throttle valve 8. . In S106, after controlling the filter temperature increase rate Rup, the ECU 10 once ends the execution of this routine.

According to the control routine described above, even when the filter regeneration control is executed and the temperature of the filter 3 is rising, the temperature of the filter 3 is allowed even if the operation state of the internal combustion engine 1 becomes an idle operation. It can be suppressed to the upper limit temperature Tlimit or lower. For this reason, it is possible to prevent the filter 3 from being overheated when the filter regeneration control is executed. Accordingly, the execution time of the filter regeneration control can be shortened as much as possible.

  In the above control routine, when the filter temperature increase rate Rup is controlled, it is preferable to control the filter temperature increase rate Rup to the upper limit value within a range where the filter arrival temperature Ta is equal to or lower than the allowable upper limit temperature Tlimit.

  According to such control, after the start of the filter regeneration control, the temperature of the filter 3 can be raised to the target temperature Tt at an earlier time while suppressing the excessive temperature rise of the filter 3.

  In this embodiment, the filter arrival temperature Ta is set to the filter arrival temperature when the operation state of the internal combustion engine 1 becomes the idle operation when the filter regeneration control is executed and the temperature of the filter 3 is rising. The filter attainment temperature Ta may be the filter attainment temperature when the engine speed of the internal combustion engine 1 is equal to or lower than a predetermined engine speed. In this case, the prescribed engine speed is not limited to the idling engine speed, and may be a threshold value of the engine speed at which it can be determined that the filter 3 may overheat.

  By setting the filter reaching temperature Ta to such a value, not only when the operation state of the internal combustion engine 1 becomes the idle operation when the filter regeneration control is executed and the temperature of the filter 3 is rising, Even when the engine speed of the engine 1 is equal to or lower than the specified engine speed, the temperature of the filter 3 can be suppressed to the allowable upper limit temperature Tlimit or lower.

  Further, the higher the altitude at the point where the vehicle travels, the lower the density of air in the atmosphere, so that the amount of heat taken away when the engine speed of the internal combustion engine 1 decreases decreases. Therefore, even if the filter temperature increase rate Rup at the time when the engine speed of the internal combustion engine 1 decreases is the same, the filter arrival temperature when the engine speed of the internal combustion engine 1 decreases is high at the vehicle travel point. It gets higher. Therefore, the target value for controlling the filter temperature increase rate Rup in the control routine may be adjusted according to the altitude of the vehicle travel point.

  Since the schematic configuration of the internal combustion engine and the intake / exhaust system thereof according to the present embodiment is the same as that of the first embodiment, the description thereof is omitted. Also in this embodiment, the filter regeneration control is executed in the same manner as in the first embodiment.

<Filter temperature rise rate control>
Here, the control routine of the filter temperature increase rate control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is executed every time the crankshaft rotates by a specified angle during the operation of the internal combustion engine 1. Note that this routine differs from the control routine for controlling the filter temperature increase rate according to the first embodiment only in that S102 is replaced with S202, and the other steps are the same. Therefore, only S202 will be described.

  In this routine, in S202, the ECU 10 determines whether or not the temperature of the filter 3 is equal to or higher than the specified temperature T0 and lower than the target temperature Tt. If an affirmative determination is made in S202, the ECU 10 proceeds to S103, and if a negative determination is made, the ECU 10 ends the execution of this routine.

Here, the specified temperature T0 is a temperature lower than the target temperature Tt, and even if the filter regeneration control is executed and the temperature of the filter 3 is increasing, if the temperature of the filter 3 is not more than the specified temperature T0, the internal combustion engine Even if the operating state of the engine 1 becomes idle operation, the temperature is such that the possibility that the filter 3 will be overheated is low.

  According to the present embodiment, even when the filter regeneration control is started and the temperature of the filter 3 is rising, the filter temperature increase rate Rup is not limited while the temperature of the filter 3 is lower than the specified temperature T0. . As a result, the temperature of the filter 3 can be raised to the target temperature Tt at an earlier time while suppressing the excessive temperature rise of the filter 3 after the start of the filter regeneration control. Accordingly, the execution time of the filter regeneration control can be shortened as much as possible.

The figure which shows schematic structure of the internal combustion engine which concerns on the Example of this invention, and its intake-exhaust system. The flowchart which shows the control routine of filter temperature increase rate control which concerns on Example 1 of this invention. The flowchart which shows the control routine of the filter temperature rise rate control which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Particulate filter 5 ... Fuel addition valve 6 ... Oxidation catalyst 8 ... Throttle valve 9 ... Exhaust differential pressure sensor 10 ... ECU
11. Crank position sensor

Claims (3)

A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
Filter regeneration control execution means for performing filter regeneration control for oxidizing and removing particulate matter deposited on the particulate filter by raising the temperature of the particulate filter to a target temperature;
PM deposition amount detection means for detecting the amount of particulate matter deposited on the particulate filter;
A temperature increase rate detecting means for detecting a temperature increase rate when the filter regeneration control is executed by the filter regeneration control executing means and the temperature of the particulate filter is rising;
When the filter regeneration control is executed by the filter regeneration control execution means and the temperature of the particulate filter is rising, the amount of particulate matter detected by the PM deposition amount detection means and the temperature increase rate detection means An arrival temperature predicting means for predicting an arrival temperature of the particulate filter when the engine speed of the internal combustion engine becomes equal to or less than a specified engine speed based on the detected temperature rise rate;
The temperature increase rate when the filter regeneration control is executed by the filter regeneration control executing means and the temperature of the particulate filter is rising is the allowable upper limit of the temperature reached by the particulate filter predicted by the reached temperature predicting means. A temperature increase rate control means for controlling the temperature to be equal to or lower than the temperature;
An exhaust gas purification system for an internal combustion engine, comprising:   2. The internal combustion engine according to claim 1, wherein the temperature rise rate of the particulate filter is controlled by the temperature rise rate control means only when the temperature of the particulate filter is equal to or higher than a specified temperature lower than the target temperature. Engine exhaust purification system.   The temperature rise rate control means controls the temperature rise rate of the particulate filter to an upper limit value within a range where the reached temperature of the particulate filter predicted by the reached temperature prediction means is equal to or lower than the allowable upper limit temperature. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2.

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