JP5323506B2 - 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 composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed 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 each flow path partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  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. Although it is necessary to regenerate, in an ordinary diesel engine operation state, there are few opportunities to obtain an exhaust temperature high enough for the particulates to self-combust.

  For this reason, for example, an oxidation catalyst formed by adding an appropriate amount of a rare earth element such as cerium to a material in which platinum is supported on alumina is integrally supported on a particulate filter and collected in the particulate filter. The oxidation reaction of the particulates is promoted by the oxidation catalyst to lower the ignition temperature, so that the particulates can be burned and removed even at an exhaust temperature lower than that of the prior art.

  However, even in such a case, in the operation region where the exhaust temperature is low, the trapped amount exceeds the processing amount of the particulates, and therefore the operation state at such a low exhaust temperature continues. There is a risk that the particulate filter will fall into an over-collected state without the particulate filter regenerating well, and the particulate filter is forcibly heated and trapped when the amount of accumulated particulate matter has increased. It is necessary to incinerate the collected particulates.

  More specifically, a flow-through type oxidation catalyst is provided in front of the particulate filter, and fuel is added upstream from the oxidation catalyst, and the added fuel is oxidized by the oxidation catalyst in front of the particulate filter. The exhaust gas heated by the reaction heat is introduced into the particulate filter, the catalyst bed temperature is raised to burn out the particulate, and the particulate filter is regenerated.

  The method for forcibly regenerating this type of particulate filter is also described in the following Patent Document 1 and Patent Document 2 by the same applicant as the present invention.

JP 2003-83139 A JP 2003-155913 A

  However, the conventional forced regeneration of the particulate filter performs post-injection at the timing of non-ignition following the main injection of fuel performed near the compression top dead center, as described in Patent Document 1 and Patent Document 2 above. In general, fuel is added and added, and if fuel is added by post injection in this way, the dispersibility of the added fuel is improved by good agitation in the cylinder and the subsequent turbocharger. Since the heat of reaction can be generated efficiently by the oxidation catalyst, the particulate filter can be forced to regenerate even from an operating region where the exhaust temperature is relatively low. Some of the fuel that has flowed down flows into the oil pan at the bottom of the engine, causing the engine oil to dilute. There is a disadvantage that lead to a deterioration of the fuel consumption by flowing down to the minute is wasted.

  In addition, a method of adding fuel by inserting an injector through the exhaust pipe upstream of the oxidation catalyst as a fuel addition means and directly injecting the fuel into the exhaust pipe using the injector has already been proposed. If fuel addition by direct injection into the pipe is adopted, there is an advantage that dilution of engine oil and deterioration of fuel consumption as described above can be avoided, but since dispersibility is inferior compared to the case of post injection, There was a demerit that fuel addition could not be started unless it was from an operating region where the exhaust temperature was higher than when fuel was added by post injection.

  That is, when fuel is directly injected into the exhaust pipe by an injector in an operating region where the exhaust temperature is low, the added fuel is transported to the exhaust gas in the form of a mist, and is processed into an oxidation catalyst whose catalytic activity has not sufficiently increased. Contrary to the original intention, the mist content of the added fuel that cannot be absorbed accumulates, and contrary to the original intention, the catalyst bed temperature of the oxidation catalyst is lost due to the heat of vaporization of the added fuel and the like, and the activity of the oxidation catalyst is lost. There was a fear of being.

  The present invention has been made in view of the above circumstances, and by selectively switching between post-injection and direct injection into the exhaust pipe, the particulate filter is forcibly regenerated from operating conditions at low exhaust temperatures. The purpose is to greatly reduce engine oil dilution and fuel consumption deterioration.

In the present invention, the fuel is added to the exhaust gas upstream of the catalyst regeneration type particulate filter provided in the middle of the exhaust pipe with the oxidation catalyst provided in the previous stage, and the added fuel is oxidized on the previous stage oxidation catalyst. In a method for forcibly regenerating the particulate filter by burning the collected particulate in the downstream particulate filter by the reaction heat generated when the reaction occurs, the activity of the oxidation catalyst reaches a level sufficient to treat the added fuel. A temperature corresponding to the catalyst bed temperature of the oxidation catalyst that can be determined to be reached is determined as the first reference temperature, and after a slight time delay, the catalyst bed temperature of the downstream oxidation catalyst is set as the first reference temperature. the exhaust temperature capable determined as the second reference temperature, the first of the exhaust temperature measured between the oxidation catalyst and the particulate filter over the first reference temperature And when the second condition that the exhaust temperature measured near the engine upstream of the oxidation catalyst is equal to or higher than the second reference temperature is not satisfied, When either of the conditions is satisfied, post-injection is added at the non-ignition timing following the main injection of fuel near the compression top dead center, and fuel is added. The fuel addition is performed by stopping the injection and directly injecting the fuel into the exhaust pipe upstream of the oxidation catalyst.

  That is, the exhaust temperature measured between the oxidation catalyst and the particulate filter can be regarded substantially as the catalyst bed temperature of the oxidation catalyst, and the exhaust temperature measured here is above the first reference temperature. By checking whether or not there is, it is determined whether or not the catalytic activity of the oxidation catalyst has reached a level sufficient to treat the added fuel.

  The exhaust temperature measured at a position near the engine upstream of the oxidation catalyst is an exhaust temperature that eventually affects the catalyst bed temperature of the downstream oxidation catalyst, and the measured exhaust temperature is equal to or higher than the second reference temperature. To determine whether the catalytic activity of the oxidation catalyst can be maintained at a level sufficient to treat the added fuel until after a slight time delay.

  Therefore, when neither the first condition nor the second condition is satisfied, the catalytic activity of the current oxidation catalyst does not reach a level sufficient to process the added fuel, and even after a slight time delay Since it is considered that the required level is not expected to be exceeded, in such a case, it is inappropriate to perform the fuel addition itself, and it is necessary to reserve the fuel addition.

  In addition, when only one of the first condition and the second condition is satisfied, the current catalytic activity of the oxidation catalyst does not reach a level sufficient to process the added fuel, but it is necessary after a slight time delay. Or the current catalytic activity of the oxidation catalyst has reached a level sufficient to process the added fuel, but will fall below the required level after a slight time delay. Since an expected case is conceivable, direct injection into the exhaust pipe having poor dispersibility should be avoided in such a case, and post-injection having good dispersibility needs to be selected.

  Furthermore, when the first and second conditions are met simultaneously, the catalytic activity of the current oxidation catalyst has reached a level sufficient to process the added fuel, and is necessary even after a slight time delay. In this case, even if direct injection into the exhaust pipe is selected, there is no possibility of losing the activity of the oxidation catalyst, and post injection is stopped. The fuel can be added by directly injecting the fuel into the exhaust pipe.

  According to the above-described method for regenerating a particulate filter of the present invention, post-injection with good dispersibility is limitedly used under conditions where the activity in the preceding oxidation catalyst is relatively low, and the activity in the preceding oxidation catalyst is relatively Since switching from post-injection to direct injection into the exhaust pipe is performed under high conditions, the particulate filter is operated from a low exhaust temperature operating condition as in the case of the forced regeneration of the particulate filter performed only by conventional post-injection. While starting the forced regeneration, engine oil dilution and fuel consumption deterioration can be greatly suppressed, and the mist of the added fuel is continuously attached to the low-activity oxidation catalyst by direct injection into the exhaust pipe. Thus, it is possible to achieve an excellent effect that the possibility of losing the activity of the oxidation catalyst can be avoided.

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 by the control apparatus of FIG.

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

  FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is an intake pipe 5 And the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 to be cooled, and the intake air 4 further flows from the intercooler 6 to the intake manifold 7. It is guided and distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1).

  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 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

  A filter case 12 is interposed in the middle of the exhaust pipe 11, and a catalyst regeneration type particulate filter 13 that integrally carries an oxidation catalyst is provided in the rear stage in the filter case 12. The particulate filter 13 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths partitioned in a lattice shape are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas 9 which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  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 an exhaust gas is disposed between the oxidation catalyst 14 and the particulate filter 13. A temperature sensor 15 for measuring the temperature of the gas 9 is provided, and a temperature signal 15a of the temperature sensor 15 is input to a control device 20 constituting an engine control computer (ECU: Electronic Control Unit). .

  Since this control device 20 also serves as an engine control computer, it is also responsible for control related to fuel injection. More specifically, the control device 20 detects an accelerator opening as a load of the diesel engine 1 ( A fuel injection device that injects fuel into each cylinder 8 of the diesel engine 1 based on an accelerator opening signal 16a from the load sensor) and a rotation speed signal 17a from the rotation sensor 17 that detects the engine rotation speed of the diesel engine 1. A fuel injection signal 18 a is output to the engine 18.

  Here, the fuel injection device 18 is composed of a plurality of injectors 19 provided for each cylinder 8, and the electromagnetic valves of these injectors 19 are appropriately controlled to open by the fuel injection signal 18a. The injection timing (valve opening timing) and the injection amount (valve opening time) are appropriately controlled.

  Further, in the present embodiment, an injector 21 as a fuel addition means different from the fuel injection device 18 is attached to the inlet side of the filter case 12, and the injector 21 is received by a command signal 21 a from the control device 20. However, the fuel can be directly injected into the exhaust gas 9 in the exhaust pipe 11.

  Further, a temperature sensor 22 different from the temperature sensor 15 is provided at a position close to the diesel engine 1 upstream of the fuel addition position of the injector 21, and the temperature signal 22 a of the temperature sensor 22 is also the control device. 20 is input.

  The control device 20 extracts the rotational speed of the diesel engine 1 based on the rotational speed signal 17a from the rotational sensor 17, and is determined when the fuel injection signal 18a is determined based on the accelerator opening signal 16a from the accelerator sensor 16. The basic fuel generation amount based on the current operating state of the diesel engine 1 is estimated from the particulate generation map based on the rotational speed and the fuel injection amount. The final generation amount is obtained by multiplying the total generation amount by a correction coefficient considering various conditions related to the generation of particulates and subtracting the processing amount of the particulates in the current operating state. The amount of particulate accumulation is estimated by integrating the amount from time to time.

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

  Further, in the control device 20, when it is estimated that the amount of accumulated particulates has reached a predetermined target value, the post-injection and the exhaust pipe 11 are started in order to start the forced regeneration of the particulate filter 13. One of the direct injections is selected and executed, but the first condition is that the exhaust gas temperature measured by the temperature sensor 15 between the oxidation catalyst 14 and the particulate filter 13 is equal to or higher than the first reference temperature. And the second condition that the exhaust temperature measured by the temperature sensor 22 at a position close to the diesel engine 1 upstream from the oxidation catalyst 14 is equal to or higher than the second reference temperature, and both the first condition and the second condition are determined. Non-ignition following main injection of fuel near compression top dead center when fuel addition is reserved when either is not met and either the first or second condition is met The fuel is added by adding post injection at the timing, and when the first condition and the second condition are simultaneously satisfied, the post injection is stopped and the fuel is directly injected into the exhaust pipe 11 upstream of the oxidation catalyst 14. In this way, fuel is added.

  That is, the exhaust temperature measured between the oxidation catalyst 14 and the particulate filter 13 can be regarded substantially as the catalyst bed temperature of the oxidation catalyst 14, and the exhaust temperature measured here is the first reference. By checking whether or not the temperature is equal to or higher than the temperature, it is determined whether or not the catalytic activity of the oxidation catalyst 14 has reached a level sufficient for processing the added fuel.

  The exhaust temperature measured at a position near the diesel engine 1 upstream from the oxidation catalyst 14 is an exhaust temperature that eventually affects the catalyst bed temperature of the downstream oxidation catalyst 14, and the exhaust temperature measured here is the first exhaust temperature. By checking whether or not the temperature is equal to or higher than the two reference temperatures, it is determined whether or not the catalytic activity of the oxidation catalyst 14 can be maintained at a level sufficient to process the added fuel until after a slight time delay.

  The first reference temperature defined here corresponds to the catalyst bed temperature of the oxidation catalyst 14 at which it can be determined that the activity of the oxidation catalyst 14 has reached a level sufficient for processing the added fuel. The second reference temperature is appropriately determined as an exhaust temperature at which the catalyst bed temperature of the downstream oxidation catalyst 14 can be set as the first reference temperature after a slight time delay. It is what was done.

  Therefore, when neither the first condition nor the second condition is satisfied, the current catalytic activity of the oxidation catalyst 14 does not reach a level sufficient to process the added fuel, and after a slight time delay. However, in this case, it is inappropriate to perform the fuel addition, and it is necessary to reserve the fuel addition.

  When only one of the first condition and the second condition is satisfied, the current catalytic activity of the oxidation catalyst 14 does not reach a level sufficient to process the added fuel, but after a slight time delay. Either the expected level is expected to be exceeded, or the current catalytic activity of the oxidation catalyst 14 has reached a level sufficient to process the added fuel, but will fall below the required level after a slight time delay. Since a case that is expected can be considered, direct injection into the exhaust pipe 11 with poor dispersibility should be avoided in such a case, and it is necessary to select post-injection with good dispersibility.

  Further, when the first condition and the second condition are simultaneously satisfied, the current catalytic activity of the oxidation catalyst 14 has reached a level sufficient to process the added fuel, and is necessary even after a slight time delay. In such a case, even if direct injection into the exhaust pipe 11 is selected, there is no fear that the activity of the oxidation catalyst 14 is lost. It is possible to add fuel by stopping post injection and directly injecting fuel into the exhaust pipe 11.

  The specific control procedure in the control device 20 is as shown in the flowchart of FIG. 2. First, in step S1, based on the temperature signals 15a and 22a from the temperature sensors 15 and 22, the oxidation catalyst 14 and the particulate filter 13 Between the first condition that the exhaust temperature measured by the temperature sensor 15 is equal to or higher than the first reference temperature, and the exhaust temperature measured by the temperature sensor 22 at a position close to the diesel engine 1 upstream from the oxidation catalyst 14 is the second. It is determined whether or not the second condition of the reference temperature or higher is simultaneously satisfied.

  If the determination in the previous step S1 is “YES”, the process proceeds to step S2 where the direct injection into the exhaust pipe 11 is selected and the command signal for executing the direct injection into the exhaust pipe 11 is selected. 21 a is output from the control device 20 toward the injector 21.

  If the determination in step S1 is “NO”, the process proceeds to step S3, and the exhaust temperature measured by the temperature sensor 15 between the oxidation catalyst 14 and the particulate filter 13 is the first reference temperature. Whether the above first condition and the second condition that the exhaust temperature measured by the temperature sensor 22 at a position close to the diesel engine 1 upstream from the oxidation catalyst 14 is equal to or higher than the second reference temperature are not satisfied. Is determined.

  If the determination in the previous step S3 is “YES”, the process proceeds to step S4 and the reserve of fuel addition is determined. If “NO”, the process proceeds to step S5 and post-injection is selected. Then, the fuel injection signal 18 a for executing the post injection is output toward the fuel injection device 18.

  The above will be described over time by taking the cold start as an example. At the beginning of the start, since neither the first condition nor the second condition is satisfied, the execution of fuel addition is suspended, but eventually the diesel engine When the exhaust gas temperature measured at a position close to the diesel engine 1 upstream from the oxidation catalyst 14 is higher than the second reference temperature and the second condition is satisfied, Post-injection is started prior to direct injection, and the fuel added by the post-injection is well agitated in the cylinder 8 or the subsequent turbocharger 2 or the like and reaches the preceding oxidation catalyst 14 in a state of good dispersibility. As a result, an oxidation reaction is efficiently caused by the oxidation catalyst 14 to raise the temperature of the exhaust gas 9 by the reaction heat, and the exhaust gas 9 flows into the particulate filter 13 at the subsequent stage so Catalyst bed temperature of the filter 13 is increased.

  As the oxidation reaction of the added fuel proceeds in the oxidation catalyst 14, the exhaust temperature measured between the oxidation catalyst 14 and the particulate filter 13 also reaches the first reference temperature, whereby the first condition and the second condition As a result, the post injection is stopped and the direct injection of fuel into the exhaust pipe 11 is started.

  At this time, since the catalytic activity of the oxidation catalyst 14 in the previous stage has already increased to a predetermined level due to fuel addition by post injection, even if the dispersibility of the added fuel is reduced by post injection, the added fuel is treated. There is no fear of remaining without being exhausted, all of which is treated with the oxidation catalyst 14 and effectively used for forced regeneration of the particulate filter 13, and a part of the oil is used as in the case of post injection. There is no longer a problem that the engine oil is diluted by dropping into the pan and deteriorating fuel consumption.

  When the exhaust temperature decreases due to deceleration or the like and only one of the first condition and the second condition is satisfied, the post-injection is switched again, and the direct injection into the exhaust pipe 11 by the injector 21 is performed. Of course, it will be canceled.

  Therefore, according to the above embodiment, the post-injection with good dispersibility is limitedly used under the condition where the activity in the preceding oxidation catalyst 14 is relatively low, and under the condition where the activity in the preceding oxidation catalyst 14 is relatively high. Since the post-injection is switched to the direct injection into the exhaust pipe 11, the particulate filter 13 is operated from an operating condition with a low exhaust temperature as in the case of the forced regeneration of the particulate filter 13 performed only by the conventional post-injection. While starting forced regeneration, dilution of engine oil and deterioration of fuel consumption can be greatly suppressed, and the mist of the added fuel continues to the oxidation catalyst 14 having low activity due to direct injection into the exhaust pipe 11. It is possible to avoid the possibility that the oxidation catalyst 14 may be deposited and lose the activity of the oxidation catalyst 14 beforehand.

  Note that the method for regenerating a particulate filter of the present invention is not limited to the above-described embodiments, and it is needless to say that various changes can be made without departing from the scope of the present invention.

1 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 9 Exhaust gas 11 Exhaust pipe 13 Particulate filter 14 Oxidation catalyst 15 Temperature sensor 15a Temperature signal 18 Fuel injection apparatus 18a Fuel injection signal 19 Injector 20 Control apparatus 21 Injector 21a Command signal 22 Temperature sensor 22a Temperature signal

Claims (1)

The fuel is added to the exhaust gas on the upstream side of the catalyst regeneration type particulate filter provided in the middle of the exhaust pipe with the oxidation catalyst provided in the previous stage, and the added fuel undergoes an oxidation reaction on the previous stage oxidation catalyst. In the method for forcibly regenerating the particulate filter by burning the collected particulate in the downstream particulate filter by reaction heat, the activity of the oxidation catalyst has reached a level sufficient to treat the added fuel. A temperature corresponding to the catalyst bed temperature of the oxidation catalyst that can be determined is determined as the first reference temperature, and after a slight time delay, the catalyst bed temperature of the downstream oxidation catalyst can be set as the first reference temperature. determine the exhaust temperature as a second reference temperature, exhaust temperature and a first condition that a first reference temperature or more, which is measured between the oxidation catalyst and a particulate filter, before Fuel addition is reserved when neither of the second conditions that the exhaust temperature measured near the engine upstream of the oxidation catalyst is above the second reference temperature are satisfied, and either the first condition or the second condition is satisfied At the time of non-ignition following the main injection of fuel near the compression top dead center, fuel addition is performed, and post injection is stopped when the first and second conditions are satisfied at the same time Then, the particulate filter is regenerated by directly injecting the fuel into the exhaust pipe upstream of the oxidation catalyst.

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