JP5487723B2 - Particulate filter regeneration method - Google Patents

Description

  The present invention relates to a method for regenerating a particulate filter.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of ceramics such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. The outlet of the passage is sealed, and only the exhaust gas that has permeated through the porous thin wall defining each flow passage is discharged downstream, while the particulates in the exhaust gas are porous. It is collected on the inner surface of the thin wall.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough to cause the particulates to self-combust. The curate filter is integrally supported.

  That is, if such a particulate filter carrying an oxidation catalyst is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at a lower exhaust temperature than in the past. It becomes possible.

  However, even when such a particulate filter is adopted, the trapped amount exceeds the processing amount of particulates in the operation region where the exhaust temperature is low, so operation at such a low exhaust temperature is required. If the state continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is attached on the inlet side of the particulate filter, and fuel is added upstream from the particulate filter when the amount of particulate accumulation increases, forcing the particulate filter to regenerate. It is considered to do.

  In other words, in this way, the particulate filter bed temperature immediately after the inflow of exhaust gas heated by the reaction heat of the high-concentration hydrocarbon generated by the fuel addition while passing through the oxidation catalyst. The particulates are burned out and the particulate filter is regenerated (see, for example, Patent Document 1 below).

  As a specific means for executing this type of fuel addition, post injection is performed at a non-ignition timing later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is common to add fuel to the exhaust gas.

  On the other hand, in a diesel engine, a part of the exhaust gas is extracted from the exhaust side and returned to the intake side, and the exhaust gas returned to the intake side suppresses combustion of fuel in the engine to lower the combustion temperature. So-called exhaust gas recirculation (EGR), which reduces the generation of NOx (nitrogen oxides) by means of this, is also performed. From the viewpoint of securing a larger amount of excess oxygen in the exhaust gas necessary for the oxidation reaction), it is generally suspended temporarily during forced regeneration.

  On the other hand, in order to achieve further exhaust purification in the future, it is considered necessary to continue exhaust gas recirculation and suppress NOx emissions even during forced regeneration. It has been confirmed by the present inventors that NOx emission can be suppressed without any problem even if exhaust gas recirculation is continued as it is during forced regeneration during normal running.

JP 2003-193824 A

  However, especially in cold districts, if the particulate filter is placed in a condition where it is difficult to maintain the particulate filter at a high temperature, such as low-temperature conditions of outside air, strong wind conditions, operating conditions with frequent engine shutdowns, etc. By continuing exhaust gas recirculation during regeneration, the excess oxygen in the exhaust gas is reduced, the oxidation reaction of the added fuel becomes inactive, and the particulate filter cannot be maintained at a high temperature, which may lead to regeneration failure. there were.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to reliably avoid a regeneration failure while suppressing the NOx emission amount during forced regeneration of a particulate filter.

The present invention is provided with an oxidation catalyst upstream of the particulate filter installed in the middle of the exhaust pipe, and adds fuel to the exhaust gas upstream from the oxidation catalyst, and the added fuel is oxidized on the oxidation catalyst of the previous stage. In the method for forcibly regenerating the particulate filter by burning the collected particulate in the downstream particulate filter with the heat of reaction at the time of reaction, a part of the exhaust gas is recirculated from the exhaust side to the intake side. While the forced regeneration of the particulate filter is executed, the forced regeneration of the particulate filter is continued until the processing amount in the particulate filter reaches the accumulation amount and it is determined that the regeneration is completed. The exhaust gas recirculation is stopped when the first condition is not satisfied, while the ignition When the second condition that down switch has not been turned off is not satisfied and means ceases the recirculation of the exhaust gas after confirming that the reproducing conditions of the particulate filter during on the next ignition switch is established To do.

Thus, in this way, forced regeneration of the particulate filter is attempted while the exhaust gas is recirculated, and when the regeneration time exceeds a predetermined time, the particulates are combined with exhaust gas recirculation. While it is judged that it is difficult to forcibly regenerate the curate filter, the exhaust gas recirculation is stopped.If the ignition switch is turned off during the forced regeneration, the exhaust gas is not recirculated when the ignition switch is turned on the next time. It is determined that it is difficult to forcibly regenerate the particulate filter while being used together, and the exhaust gas recirculation is stopped, and the forced regeneration of the particulate filter is assisted to complete it promptly.

  That is, when the first condition is not satisfied, it can be seen that the regeneration time is longer than usual, and that the removal of the collected particulates in the particulate filter is not efficiently burned away. It is estimated that the particulate filter is not maintained at a high temperature well due to the low temperature condition or strong wind condition of the outside air.

  On the other hand, if the second condition is not satisfied, it can be seen that the ignition switch was turned off during the forced regeneration of the particulate filter, and more specifically, the engine was turned off during the forced regeneration of the particulate filter. It is presumed that the fuel addition was interrupted and the temperature of the particulate filter temporarily decreased.

  Therefore, if at least one of the first condition and the second condition is not satisfied, it is assumed that the particulate filter is placed under a condition that is difficult to maintain at a high temperature. If the exhaust gas recirculation is stopped, the excess oxygen in the exhaust gas increases, and the oxidation reaction of the added fuel in the oxidation catalyst upstream of the particulate filter is activated. Will be maintained.

In the present invention, it is preferable to use a temperature raising means for raising the exhaust temperature in conjunction with stopping the exhaust gas recirculation . For example, an exhaust throttle means for appropriately reducing the exhaust flow rate as the temperature raising means. It is possible to use.

  According to the method for regenerating a particulate filter of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first aspect of the present invention, the forced regeneration of the particulate filter is performed while the exhaust gas is recirculated, and the particulate filter is difficult to maintain at a high temperature during the forced regeneration. Since exhaust gas recirculation is stopped only when it is estimated that the exhaust gas is placed underneath, the regeneration failure is suppressed while suppressing NOx emissions during forced regeneration of the particulate filter. Can be reliably avoided.

(II) According to the invention described in claim 2 of the present invention, in combination with stopping the exhaust gas recirculation, the temperature riser for raising the exhaust temperature is used in combination, thereby preventing the regeneration failure of the particulate filter. This can be avoided more reliably.

(III) According to the invention described in claim 3 of the present invention, the exhaust gas recirculation can be reduced and the exhaust gas temperature can be raised together with stopping the exhaust gas recirculation. Can be avoided more reliably.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the specific control procedure in the control apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 shows a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 passes through an intake pipe 5 and the turbocharger. 2, the intake air 4 pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7. 1 is distributed to each cylinder 8 (FIG. 1 illustrates the case of inline 6 cylinders).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 driving the turbine 2b is discharged to the exhaust pipe 11 (exhaust gas). It is designed to be discharged out of the vehicle through the flow path.

  In the middle of the exhaust pipe 11, a filter case 12 is interposed, and a catalyst regeneration type particulate filter 13 integrally supporting an oxidation catalyst is provided on the rear stage side in the filter case 12. This particulate filter 13 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are sealed. For the non-flow paths, the outlets are sealed, and only the exhaust gas 9 that has permeated through the porous thin wall defining each flow path is discharged to the downstream side.

  A flow-through type oxidation catalyst 14 having a honeycomb structure is accommodated immediately before the particulate filter 13 in the filter case 12 and is added to the exhaust gas 9 by the oxidation catalyst 14 during forced regeneration. The added fuel to be oxidized is oxidized so that the particulate filter 13 can be heated by reaction heat.

  Further, in the example shown in FIG. 1, an EGR line 15 connects between one end portion of the exhaust manifold 10 in the arrangement direction of the cylinders 8 and one end portion of the intake pipe 5 connected to the intake manifold 7. A part of the exhaust gas 9 extracted from the exhaust manifold 10 is cooled by a water-cooled EGR cooler 16 and recirculated to the intake pipe 5 via an EGR valve 17.

  Further, an exhaust throttle valve 18 (exhaust throttle means) that appropriately narrows the flow path of the exhaust pipe 11 is provided as a temperature raising means for raising the exhaust temperature near the outlet of the turbine 2 b in the exhaust pipe 11. By appropriately narrowing the flow path of the exhaust pipe 11 with the valve 18, the exhaust resistance from each cylinder 8 of the diesel engine 1 is increased to increase the pumping loss, thereby increasing the fuel injection amount so that the necessary output is generated. The exhaust temperature can be raised.

The EGR valve 17 and the exhaust throttle valve 18 are controlled to open and close by control signals 17a and 18a from a control device 19 that also serves as an engine control computer (ECU: Electronic Control Unit). Even during the forced regeneration of the particulate filter 13 to be performed, both the EGR valve 17 and the exhaust throttle valve 18 are basically kept open so that the recirculation of the exhaust gas 9 and the non-execution of the exhaust throttle can be continued. However, when the first condition that the regeneration time of the particulate filter 13 does not exceed the predetermined time is not satisfied, the recirculation of the exhaust gas 9 is stopped, while the ignition switch 22 is not turned off during the forced regeneration. When the two conditions are not satisfied, the particulates will be turned on the next time the ignition switch 22 is turned on. Reproduction condition DOO filter 13 is made after confirming that the satisfied to stop recirculation of exhaust gas 9.

  Here, since the control device 19 also serves as an engine control computer, it is also responsible for control relating to fuel injection. More specifically, the opening degree of the accelerator in the driver's seat (not shown) Fuel is supplied to each cylinder 8 of the diesel engine 1 based on a detection signal 20a from the accelerator sensor 20 that is detected as a load and a detection signal 21a that is provided at an appropriate position of the diesel engine 1 and detects the rotation speed 21a. The control signal 23a is output to the fuel injection device 23 that injects fuel.

  Here, the fuel injection device 23 is constituted by a plurality of injectors provided for each cylinder 8, and the solenoid valve of each injector is appropriately controlled to open by the control signal 23a, and the fuel injection timing is set. (Valve opening timing) and injection amount (valve opening time) are appropriately controlled.

  In the control device 19, the control signal 23a in the normal mode is determined based on the control signals 23a and 21a. On the other hand, when the forced regeneration of the particulate filter 13 is to be performed, the normal mode is switched to the regeneration mode. After the main injection of fuel performed near the compression top dead center (crank angle 0 °), post-injection is performed at a non-ignition timing (starting time range is 90 ° to 120 ° crank angle) after the compression top dead center. The control signal 23a to be performed is determined.

  That is, when post-injection is performed at the non-ignition timing later than the compression top dead center following the main injection in this way, unburned fuel (mainly HC: carbonized) in the exhaust gas 9 in the cylinder 8 by this post-injection. This unburned fuel becomes high-concentration HC gas and flows to the preceding oxidation catalyst 14 to cause an oxidation reaction, and the exhaust gas 9 heated by the reaction heat becomes the latter-stage patties. By flowing into the curative filter 13, the catalyst bed temperature of the particulate filter 13 rises, and the collected particulates inside are burned and removed.

  Further, in the control device 19, the rotational speed of the diesel engine 1 is extracted based on the detection signal 21 a from the rotation sensor 21, and is determined when the control signal 23 a is determined based on the detection signal 20 a from the accelerator sensor 20. The fuel injection amount is extracted, and the basic generation amount of particulates based on the current operation state of the diesel engine 1 is estimated from the particulate generation amount map based on the rotation speed and the injection amount. Multiply the amount by a correction factor that takes into account various conditions related to the generation of particulates, and subtract the particulate processing amount in the current operating state to obtain the final generation amount. The accumulated amount of particulates is estimated by integrating every moment.

  However, there are various ways of estimating the particulate deposition amount, and it is of course possible to estimate the particulate deposition amount by using a method other than the estimation method exemplified here.

  In the control device 19, after it is estimated that the amount of accumulated particulates has reached a predetermined target value, the exhaust gas grasped based on the detection signal 24a of the temperature sensor 24 on the particulate filter 13 entry side. The fuel injection control is switched from the normal mode to the regeneration mode after waiting for various conditions such as temperature (regeneration conditions) to be satisfied.

  That is, when a specific control procedure at the time of forced regeneration of the control device 19 is shown by a flowchart in FIG. 2, first, in step S1, both the EGR valve 17 and the exhaust throttle valve 18 are maintained in an open state, and then in step S2. It is confirmed that various conditions (regeneration conditions) such as the exhaust temperature grasped based on the detection signal 24a of the temperature sensor 24 are satisfied, and thereafter, the process proceeds to step S3 to change the fuel injection control from the normal mode to the regeneration mode. The forced regeneration of the particulate filter 13 is performed by switching.

  Then, in step S4, it is determined whether or not the reproduction time of the first condition is equal to or longer than the predetermined time. If the predetermined time is not exceeded, the process proceeds to "NO". In the next step S5, the ignition is performed during the forced reproduction of the second condition. Whether or not the switch 22 is detected to be off is determined based on the detection signal 22a. If the ignition switch 22 is not detected to be off, the process proceeds to "NO". In step S6, the particulates are based on the temperature detected by the temperature sensor 24. It is determined whether or not the regeneration of the filter 13 is completed. If it is determined that the regeneration of the particulate filter 13 is completed, the process proceeds to “YES”, the forced regeneration is terminated in step S7, and the completion of the regeneration is still determined. If not, the process proceeds to “NO” and returns to the flow from step S3.

  Here, when determining the completion of regeneration of the particulate filter 13, the combustion rate at each temperature of the collected particulates is grasped in advance by a preliminary experiment or the like, and the process proceeds based on the temperature detected by the temperature sensor 24. If the processing amount is calculated from the time, it can be determined that the regeneration of the particulate filter 13 is completed when the processing amount reaches the estimated accumulation amount.

  On the other hand, if the regeneration time exceeds the predetermined time in the previous step S4, the process proceeds to "YES". In step S8, the EGR valve 17 is closed to stop the recirculation of the exhaust gas 9, and the exhaust throttle valve 18 is closed to exhaust the exhaust gas. In step S9, the particulate filter 13 is forcibly regenerated in the same manner as in the previous step S3, and then in step S10, the temperature sensor 24 is set in the same manner as in the previous step S6. It is determined whether or not regeneration of the particulate filter 13 has been completed based on the detected temperature. If it is determined that regeneration of the particulate filter 13 has been completed, the process proceeds to “YES” to terminate forced regeneration in step S7. If the completion of reproduction is not yet determined, the process proceeds to “NO” and returns to the flow from step S9.

  If it is detected in step S5 that the ignition switch 22 is turned off, the process proceeds to “YES”. In step S11, the next ignition switch 22 is detected based on the detection signal 22a, and then the process proceeds to step S12. After confirming that various conditions (regeneration conditions) such as the exhaust temperature are satisfied as in the previous step S2, the process proceeds to the previous step S8, the EGR valve 17 is closed to stop the recirculation of the exhaust gas 9, and The exhaust throttle valve 18 is closed and exhaust throttling is performed to increase the temperature of the exhaust. In addition, since the flow after step S8 is as above-mentioned, description is omitted.

  Thus, if this is done, forced regeneration of the particulate filter 13 is attempted while the exhaust gas 9 is recirculated, and the regeneration time exceeds a predetermined time, or the ignition switch 22 is turned off during forced regeneration. In such a case, it is determined that the forced regeneration of the particulate filter 13 while using the recirculation of the exhaust gas 9 is difficult, the EGR valve 17 is closed to stop the recirculation of the exhaust gas 9, and the exhaust throttle valve 18 It is possible to increase the temperature of the exhaust gas by closing and closing the exhaust flow rate appropriately.

  That is, when the first condition is not satisfied, it can be seen that the regeneration time is longer than usual, and the removal of the collected particulates in the particulate filter 13 is not efficiently performed by combustion. It is presumed that the particulate filter 13 is not maintained at a high temperature well due to the low temperature condition or strong wind condition of the outside air.

  On the other hand, if the second condition is not satisfied, it can be seen that the ignition switch 22 is turned off during the forced regeneration of the particulate filter 13, and more specifically, during the forced regeneration of the particulate filter 13. It is estimated that the diesel engine 1 was turned off, fuel addition was interrupted, and the temperature of the particulate filter 13 was temporarily lowered.

  Therefore, when at least one of the first condition and the second condition is not satisfied, it is estimated that the particulate filter 13 is placed under a condition that is difficult to maintain at a high temperature. In this case, if the recirculation of the exhaust gas 9 is stopped, surplus oxygen in the exhaust gas 9 increases, and the oxidation reaction of the added fuel in the oxidation catalyst in the preceding stage of the particulate filter 13 is activated. 13 is well maintained at high temperature.

  Therefore, according to the above embodiment, the forced regeneration of the particulate filter 13 is performed while the exhaust gas 9 is recirculated, and the particulate filter 13 is placed under conditions that make it difficult to maintain a high temperature during the forced regeneration. Only when it is estimated that the exhaust gas 9 is recirculated, the recirculation of the exhaust gas 9 is stopped in a limited manner, so that the regeneration failure can be ensured while suppressing the NOx emission amount during the forced regeneration of the particulate filter 13. It can be avoided.

Further, when the exhaust gas recirculation of the exhaust gas 9 is stopped and the exhaust throttle valve 18 is used in combination, the exhaust gas flow rate can be reduced and the exhaust gas temperature can be raised, so that the regeneration failure of the particulate filter 13 can be more reliably performed. Can be avoided.

  The particulate filter regeneration method according to the present invention is not limited to the above-described embodiment example, and an extremely low outside air temperature is detected at the start of forced regeneration of the particulate filter. Under circumstances where it can be determined that regeneration is severe, it may be possible to select to cancel forced regeneration, and the temperature raising means may be other than the exhaust throttle means, for example, The temperature of exhaust gas may be increased by causing the fuel injection device to perform after injection at a combustible timing immediately after the main injection, and various other modifications may be made without departing from the scope of the present invention. Of course.

4 intake air 9 exhaust gas 11 exhaust pipe 13 particulate filter 14 oxidation catalyst 15 EGR line 16 EGR cooler 17 EGR valve 18 exhaust throttle valve (exhaust throttle means: temperature raising means)
19 Control device 22 Ignition switch

Claims (3)

When an oxidation catalyst is provided in the front stage of the particulate filter installed in the middle of the exhaust pipe, fuel is added to the exhaust gas upstream of the oxidation catalyst, and the added fuel undergoes an oxidation reaction on the preceding oxidation catalyst. In the method of burning the collected particulates in the downstream particulate filter by reaction heat to forcibly regenerate the particulate filter, the particulate filter while recirculating a part of the exhaust gas from the exhaust side to the intake side The forced regeneration of the particulate filter is continued until the processing amount in the particulate filter reaches the accumulation amount and it is determined that the regeneration is completed, and the regeneration time does not exceed a predetermined time. The exhaust gas recirculation is stopped when the first condition is not met, while the ignition switch is Patti There, wherein the ceasing recirculation of the exhaust gas after confirming that the reproducing conditions of the particulate filter during on the next ignition switch is established when the second condition is not satisfied that it is not turned off Curate filter regeneration method. The method for regenerating a particulate filter according to claim 1, wherein a temperature raising means for raising the exhaust gas temperature is used in combination with stopping the recirculation of the exhaust gas . The method for regenerating a particulate filter according to claim 2, wherein an exhaust throttle means for appropriately reducing an exhaust flow rate is used as the temperature raising means.

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