JP2009209788A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of considering PM (particulate matters) combustion quantity while an internal combustion engine is not in operation. <P>SOLUTION: The exhaust emission control device has a structure including a PM collecting filter arranged in an exhaust system of the internal combustion engine for collecting PM contained in exhaust emission, a stop-time PM combustion information storing means (Fig.4A) for storing at least a stop-time filter temperature of the PM collecting filter obtained when operation of the internal combustion engine is stopped and an off-time PM combustion quantity calculation means (Fig.4B) for estimating an off-time PM combustion quantity which is the quantity of PM burnt in the PM collecting filer while the engine is stopped when the internal combustion engine restarts its operation based on the stop-time filter temperature and a start-time filter temperature of the PM collecting filter acquired at a start time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus including a PM trapping filter charged into an exhaust system in order to trap particulate matter (PM) contained in exhaust gas of an internal combustion engine, and more particularly to the PM trapping device. The present invention relates to collection filter regeneration control.

  Among internal combustion engines, in particular, PM collection filters of exhaust gas purification devices provided in diesel engines generally have a honeycomb structure formed of porous ceramics, and when exhaust passes through the walls of each cell (passage). A wall flow type that collects PM is used. In the PM collection filter typified by this wall flow type, if the amount of accumulated PM is excessive, the collection capacity will decrease, or the exhaust ventilation resistance will increase and the exhaust pressure will increase. It is configured to be able to. Usually, removal of accumulated PM is realized by supporting an oxidation catalyst such as platinum on a PM collection filter and combusting PM by raising the filter temperature (for example, bed temperature).

  In such regeneration of the PM collection filter, a method of supplying unburned fuel when the filter temperature is equal to or higher than the temperature necessary for combustion is employed. However, in this method, since fuel is used, an appropriate regeneration time is determined by calculating the PM accumulation amount from the integration of the accumulation amount per unit time according to the operating state of the internal combustion engine so as not to affect the fuel consumption. Control is executed (Patent Document 1).

In this PM accumulation amount calculation control, when the internal combustion engine stops due to ignition off or the like, the PM accumulation amount at that time is stored in a non-volatile memory, and when the operation of the next internal combustion engine is restarted (ignition on or the like), Control is performed to read the PM accumulation amount stored in the memory at the previous stop as an initial value at the time of starting (see paragraphs 0059 to 0060 of Patent Document 1).
JP 2006-002672 A

  However, immediately after the internal combustion engine is stopped, the filter temperature may be higher than the PM combustible temperature. In this case, there is accumulated PM that burns before the filter temperature cools below the PM combustible temperature. In the conventional PM accumulation amount calculation control, the PM combustion amount during stoppage is not reflected in the initial value at the time of starting, so errors are accumulated, leading to a shift in the PM collection filter regeneration timing determination.

  The present invention is based on such a technical background and proposes an exhaust emission control device that can take into account the amount of PM combustion while the internal combustion engine is stopped.

  An exhaust emission control device proposed in the present invention includes a PM collection filter that is inserted into an exhaust system of an internal combustion engine and collects PM contained in the exhaust, and the PM obtained when the internal combustion engine stops operating. Stop PM combustion information storage means for storing at least the filter temperature when the collection filter is stopped, and when the internal combustion engine restarts operation, the stop filter temperature and the start of the PM collection filter obtained at the start And a stopped PM combustion amount calculation means for estimating a stopped PM combustion amount that is the amount of PM burned during the stop in the PM collection filter based on the hour filter temperature.

  According to the exhaust gas purification apparatus according to the above proposal, the PM combustion amount during stop according to the filter temperature when the internal combustion engine is stopped is estimated by the PM combustion amount calculation means during stop. Therefore, the in-stop PM combustion amount estimated by the in-stop PM combustion amount calculation means is reflected in the PM accumulation amount calculated up to the previous stop at the time of restarting operation, and the PM deposition after the reflection is performed. If the amount is used as the initial value at the time of starting, it is possible to execute the PM accumulation amount calculation control with higher accuracy in consideration of the PM combustion during the stop of the internal combustion engine.

FIG. 1 shows a configuration example of an exhaust emission control device according to an embodiment of the present invention. As an example of the internal combustion engine, a common rail type diesel engine provided with an exhaust turbocharger is illustrated.
The intake system of the diesel engine 1 is provided with an airflow sensor 2, a compressor 3 a of a turbocharger 3, an intercooler 4, and an intake throttle 5 in order from the intake upstream side, and is sucked into a cylinder through an intake manifold having a surge tank 6. Air flows in. The fuel injection system includes a supply pump 7 and a common rail 8, pressurizes the fuel, and injects the fuel from the injection nozzle 9 into the cylinder. Furthermore, the diesel engine 1 of this example includes an EGR cooler 10 and an EGR valve 11 as an exhaust gas recirculation (EGR) device that recirculates exhaust gas from the exhaust manifold to the intake manifold.

  In the exhaust system of the diesel engine 1, a turbine 3 b of the turbocharger 3 and an oxidation catalyst 12 for selective catalytic reduction (SCR) are arranged in order from the exhaust upstream, and downstream of the oxidation catalyst 12, A DPF (Diesel Particulate Filter) 20 is inserted as a wall flow type PM collection filter. Although not shown, an SCR reducing agent injection nozzle, a selective reduction catalyst, and the like are disposed downstream of the DPF 20, and an exhaust purification device that purifies NOx and PM is provided.

  An inlet temperature sensor 21 for measuring the inlet temperature of the exhaust is disposed at the exhaust inlet of the DPF 20, and an outlet temperature sensor 22 for measuring the outlet temperature of the exhaust is provided at the exhaust outlet of the DPF 20. . An airflow sensor 23 for measuring the exhaust flow rate is provided at the exhaust outlet of the DPF 20, and a differential pressure sensor 24 for measuring a differential pressure between the exhaust inlet and the exhaust outlet is also provided.

  These sensors and measurement signals of the water temperature sensor 25 that measures the cooling water temperature of the engine 1 are input to an ECU (electronic control unit) 30, and the operation of the engine 1 is controlled by the ECU 30.

  The ECU 30 of this embodiment operates as filter temperature calculation means for calculating the filter temperature (here, the bed temperature) of the DPF 20 based on the output values of the inlet temperature sensor 21, the outlet temperature sensor 22 and the airflow sensor 23. The functional block diagram is shown in FIG.

  The filter temperature calculation means includes a response delay filter processing unit 31, a time constant calculation unit 32, a correction value calculation unit 33, a 1 / Z conversion unit 34, and an addition unit 35. The response delay filter processing unit 31 inputs the output value of the inlet temperature sensor 21 and calculates the time constant calculated by the time constant calculation unit 32 based on the exhaust flow rate by the airflow sensor 23. On the other hand, the output value of the outlet temperature sensor 22 is input to the correction value calculation unit 33 and is calculated as a filter temperature value input via the 1 / Z conversion unit 34. Then, the adder 35 corrects the output value of the response delay filter processor 31 with the correction value by the correction value calculator 33, and outputs the filter temperature. That is, the bed temperature can be estimated as the filter temperature of the DPF 20 using the inlet temperature and the outlet temperature of the DPF 20.

  The relationship of the PM combustion amount when the engine 1 stops with respect to the estimated filter temperature will be described with reference to FIG. FIG. 3 is a time chart from the stop of operation to the restart shown with time on the horizontal axis.

  The ECU 30 executes stop control of the engine 1 when ignition off is detected at t1, and then executes start control of the engine 1 when ignition on is detected at t2 (FIG. 3A). The filter temperature changes as shown in FIG. 3B during the stop period t1 to t2 from the stop to the restart. That is, when the filter temperature becomes t1 when the temperature exceeds the PM combustible temperature of 500 ° C., for example, there is a time lag Δt from t1 to t3 until the filter temperature cools to the PM combustible temperature or less after the stop. To do. Therefore, during this Δt, there is a stopped PM combustion amount ΔPM in which the PM accumulated in the DPF 20 burns.

  As shown in FIG. 3C, in the prior art, when the engine 1 is stopped, the PM accumulation amount calculated up to t1 is stored in a nonvolatile memory. Then, as indicated by the dotted line in the figure, at the time of restarting operation t2, the control is performed to read the PM accumulation amount stored in the memory as the initial value at the time of starting. Since the PM accumulation amount read at this time is deviated by the PM combustion amount ΔPM during stoppage from the actual PM accumulation amount indicated by the solid line in the figure, the PM accumulation amount accumulated thereafter is ΔPM with respect to the actual value. It will change with an error of minutes.

  The ECU 30 according to the present embodiment operates as a stop PM combustion information storage unit and a stop PM combustion amount calculation unit, thereby estimating the stop PM combustion amount ΔPM and suppressing a PM accumulation amount error after restarting operation. FIG. 4 and FIG. 5 illustrate a flowchart of the stop-time PM combustion information storage means and the stop-time PM combustion amount calculation means executed by the ECU 30.

  As shown in FIG. 4A, the ECU 30 that operates as the stop-time PM combustion information storage means obtains the filter temperature calculation means when the ignition switch is confirmed to be off and the operation of the engine 1 is stopped (S1). The filter temperature of the DPF 20 is stored in a non-volatile memory (such as an EEPROM) as the filter temperature at the time of stop (S2). Further, in this example, in this step S2, the stop-time cooling water temperature, the stop-time oxygen concentration remaining in the DPF 20, and the stop-time PM accumulation amount accumulated in the DPF 20 at the stop are also stored in the memory. To remember.

  The cooling water temperature at the time of stop is acquired from the water temperature sensor 25 shown in FIG. The stop oxygen concentration is acquired based on the exhaust flow rate measured by the airflow sensor 23. In the case of this example, the oxygen concentration by the airflow sensor 23 is further corrected on the basis of the engine speed (or load) at the time of stoppage to calculate a more accurate residual oxygen concentration. The PM accumulation amount at the time of stop is the PM accumulation amount that the ECU 30 has calculated until the engine 1 is stopped.

  After storing the PM combustion information at the time of stop, when the ignition switch is turned on by restarting the operation, the ECU 30 operates as a PM combustion amount calculation means during stop as the engine 1 is started.

  As shown in FIG. 4B, when the ignition on is confirmed (S3), the ECU 30 stops PM combustion information stored in step S2, that is, the stop filter temperature, the stop cooling water temperature, the stop oxygen concentration, The PM accumulation amount at the time of stop is read (S4). Subsequently, the ECU 30 acquires the start-time coolant temperature measured by the water temperature sensor 25 as start-up information necessary for calculating the PM combustion amount during stoppage (S5).

  When the stop-time PM combustion information and the start-time information are obtained, the ECU 30 first determines whether PM combustion is occurring during the stop based on the stop-time filter temperature (S6). That is, by determining whether or not the stop-time filter temperature is equal to or higher than a threshold value, for example, a PM combustible temperature of 500 ° C., it is determined whether or not the subsequent PM combustion amount calculation is executed. If the stop-time filter temperature has not reached the PM combustible temperature, the ECU 30 ends without executing the stop-time PM combustion amount calculation.

  On the other hand, if, as a result of step S6, it is determined that there is PM combustion during stoppage, the ECU 30 continues to execute the PM combustion amount calculation during stoppage (S7). FIG. 5 shows a flow of the stopped PM combustion amount calculation step S7.

  The ECU 30 that executes the calculation of the PM combustion amount during stoppage first corrects the stop-time filter temperature based on the stop-time coolant temperature and the start-up coolant temperature, and estimates the start-up filter temperature (S10). If the filter temperature at start can be estimated, the stop time from stop to start can be estimated.

  As shown in FIG. 3B, the cooling water temperature gradually decreases after the engine 1 is stopped. Therefore, if the difference in how much the cooling water temperature at the time of start is lower than the cooling water temperature at the time of stop is obtained, the filter temperature at the time of start can be estimated from the filter temperature profile of FIG. 3B. The filter temperature profile shown in FIG. 3B is determined for each stop-time filter temperature by a temperature transition obtained by simulation. Therefore, if the filter temperature at stop is known, the filter temperature profile is determined, and if the difference between the coolant temperature at stop and the coolant temperature at start is found, this difference corresponds to the time from stop, so it is applicable on the profile. The filter temperature to be performed can be estimated as the starting filter temperature. That is, if a map of the cooling water temperature at the stop and the cooling water temperature at the start and the filter temperature at the stop is stored, the filter temperature at the stop is corrected based on the cooling water temperature at the stop and the cooling water temperature at the start. Thus, the starting filter temperature can be estimated.

  When the stop filter temperature and the start filter temperature (time from start to stop) are determined in this way, the filter temperature profile curve and PM combustible temperature between the stop filter temperature and the start filter temperature are determined. Can be calculated as the PM combustion amount during stoppage.

  Thereafter, the ECU 30 reads out the stop oxygen concentration and the stop PM deposition amount (S11), and stops the stop based on the stop filter temperature, the start filter temperature, the stop oxygen concentration, and the stop PM deposition amount. The PM combustion amount is calculated (S12). Specifically, the basic value of the PM combustion amount during stoppage is calculated from the filter temperature during stoppage and the filter temperature during start-up. And this basic value is corrected by the oxygen concentration at the time of stop which changes with the operation state at the time of stop. For example, if the engine speed at the time of stop is high, the oxygen concentration at the time of stop becomes deep and the combustion speed becomes high. Conversely, if the engine speed is low, the oxygen concentration at stop becomes thin and the combustion speed becomes low. Therefore, the basic value is increased or decreased according to the oxygen concentration at the time of stopping. Further, since the combustion speed also changes depending on the amount of accumulated PM, the basic value is corrected by a variable corresponding to the PM accumulation amount at the time of stoppage.

  The ECU 30 operates as a PM accumulation amount calculation means together with the calculation of the PM combustion amount during stoppage. For example, the ECU 30 executes the flowchart of FIG. 6 to calculate the PM accumulation amount in the DPF 20 after the engine 1 is started based on the PM combustion amount during stoppage. Calculate.

  The ECU 30 confirming that the ignition switch is turned on (S20) executes the PM emission amount calculation S21) and the PM combustion amount calculation (S22). That is, the PM discharge amount is an inflow amount into the DPF 20 and is calculated by multiplying the exhaust flow rate by the airflow sensor 23 by the PM concentration in the exhaust gas, and the initial value is zero. The PM concentration in the exhaust can be calculated as a function of the engine operating state, for example, the rotation speed and the load. The PM combustion amount is the amount of PM combustion combusted in the DPF 20 during operation, and can be calculated from the filter temperature obtained by the filter temperature calculation means described above, the current PM accumulation amount, and the oxygen concentration in the exhaust gas. . The oxygen concentration in the exhaust gas is obtained from the exhaust gas flow rate by the airflow sensor 23 and the engine operating state (rotation speed, load). The ECU 30 uses the during-stop PM combustion amount in step S7 as the initial value of this PM combustion amount.

  The ECU 30 calculates the PM accumulation amount in the DPF 20 based on the PM emission amount and the PM combustion amount (S23). In this step S23, the PM discharge amount is multiplied by a variable corresponding to the filter temperature of the DPF 20, thereby calculating an increase in the accumulation amount according to the operating state. Then, the PM accumulation amount is integrated by adding the accumulation amount increase to the current PM accumulation amount and subtracting the PM combustion amount. At the initial value at the time of starting, the PM emission amount is zero, the PM combustion amount is the PM combustion amount during stoppage, and the PM deposition amount during stoppage is used as the PM accumulation amount. Therefore, at the start, a PM accumulation amount at start is provided by subtracting the PM combustion amount during stoppage from the PM accumulation amount at stop, and the subsequent accumulation is executed with the PM accumulation amount at start as an initial value.

  After the PM accumulation amount calculation, it is confirmed that the ignition switch is turned off (S24), and the PM emission amount and PM combustion amount calculation are repeated until the ignition switch is not turned off, and the flow of FIG. 4 is started when the ignition is off.

  The ECU 30 executes regeneration processing of the DPF 20 as regeneration control means when the PM accumulation amount reaches a predetermined value based on the PM accumulation amount calculated as the PM accumulation amount calculation means in this way. Since this reproduction process is described in, for example, the above-mentioned document such as Patent Document 1, it is omitted here.

The schematic diagram of the diesel engine which showed the example of composition of the exhaust gas purification device. The functional block diagram explaining a filter temperature calculating means. The chart explaining transition of the filter temperature and cooling water temperature during a stop. The flowchart explaining the PM combustion information storage means (A) at the time of stop and the PM combustion amount calculation means (B) during the stop. The flowchart explaining the detail of the PM combustion amount calculation step during stop of FIG. 7 is a flowchart for explaining PM accumulation amount calculation means.

Explanation of symbols

1 Internal combustion engine (diesel engine)
20 PM collection filter (DPF)
21 Inlet temperature sensor 22 Outlet temperature sensor 23 Air flow sensor 24 Differential pressure sensor 25 Water temperature sensor 30 ECU

Claims (8)

A PM collection filter that is inserted into the exhaust system of the internal combustion engine and collects particulate matter contained in the exhaust;
A stop-time PM combustion information storage means for storing at least a stop-time filter temperature of the PM collection filter obtained when the internal combustion engine stops operation;
When the internal combustion engine resumes operation, particles burned during the stop in the PM collection filter based on the filter temperature at the stop and the filter temperature at the start of the PM collection filter obtained at the start An in-stop PM combustion amount calculation means for estimating an in-stop PM combustion amount that is an amount of particulate matter
An exhaust emission control device comprising: The stop PM combustion information storage means also stores a stop coolant temperature measured when the internal combustion engine stops operation,
The stopping PM combustion amount calculating means corrects the stopping filter temperature based on the stopping cooling water temperature and the starting cooling water temperature measured at starting, and estimates the starting filter temperature. The exhaust emission control device according to claim 1. The stop PM combustion information storage means also stores a stop oxygen concentration in the PM collection filter obtained when the internal combustion engine stops operation,
3. The exhaust emission control device according to claim 1, wherein the during-stop PM combustion amount calculation unit corrects the during-stop PM combustion amount based on the stop-time oxygen concentration.   The during-stop PM combustion amount calculation means uses the particulate matter accumulation amount in the PM collection filter calculated until the internal combustion engine stops operation as the stop-time PM accumulation amount, according to the stop-time PM accumulation amount. The exhaust emission control device according to any one of claims 1 to 3, wherein the PM combustion amount during stoppage is corrected.   5. The stop PM combustion amount calculation means performs the estimation of the stop PM combustion amount when the stop filter temperature is equal to or higher than a predetermined threshold value. The exhaust emission control device according to item.   The system further comprises PM accumulation amount calculation means for calculating the accumulation amount of particulate matter in the PM collection filter after the internal combustion engine is started based on the PM combustion amount during stoppage. The exhaust emission control device according to any one of claims 1 to 5. The PM accumulation amount calculating means includes:
Subtracting the PM combustion amount during stoppage from the particulate matter accumulation amount in the PM collection filter calculated until the internal combustion engine stops operation, and calculating the PM deposition amount at start-up;
The particulate matter accumulation amount after the start is calculated by adding an increment corresponding to an operating state after the internal combustion engine is started with the PM deposition amount at the start as an initial value. 6. An exhaust emission control device according to 6.   The regeneration control means for executing regeneration processing of the PM collection filter based on the accumulation amount of the particulate matter calculated by the PM deposition amount calculation means is further configured. The exhaust emission control device according to claim 7.

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