JP4572762B2 - Engine exhaust purification system - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an exhaust emission control device for an engine including a particulate filter mainly used for exhaust gas aftertreatment of a diesel engine, and more specifically, estimates an ash accumulation amount on the particulate filter. Related to technology.

Conventionally, a particulate filter formed by molding ceramic or the like into a honeycomb monolith has been used to collect particulate matter (hereinafter referred to as “particulate”) discharged from a diesel engine from the exhaust. .
If the particulates are accumulated in an amount exceeding the allowable amount with respect to the particulate filter, clogging occurs, the exhaust pressure is increased, and the drivability is adversely affected.

Therefore, the accumulated particulates are incinerated periodically to prevent clogging, but a component that cannot be removed by the incineration for regeneration but remains on the filter (hereinafter referred to as “ash”) is there.
In Patent Document 1, an ash accumulation amount is estimated from a travel distance, and a final particulate accumulation amount is obtained by subtracting the ash accumulation amount from a particulate accumulation amount estimated from a differential pressure across the filter. .
JP 2004-21650 A

By the way, conventionally, assuming that the pressure loss due to ash deposition occurs in the same way as the pressure loss due to particulate deposition, the ash deposition amount estimated based on the travel distance is subtracted from the deposition amount estimated from the differential pressure across the filter. By doing so, the amount of particulate deposition was estimated.
However, particulates and ash have different accumulation distributions on the filter, and particulates accumulate on the entire filter (inside and on the wall), whereas ash mainly accumulates at the downstream closed end of the filter, and ash accumulation. Changes the effective capacity of the particulate filter.

For this reason, in the conventional apparatus, the larger the ash accumulation amount, the greater the estimated error in the particulate accumulation amount.
If an estimation error occurs in the accumulation amount of the particulates, the regeneration process cannot be performed at an appropriate timing, the particulates are excessively deposited on the filter, or the fuel efficiency is lowered due to the wasteful regeneration process.

  Therefore, in consideration of the reduction of the filter effective capacity due to ash deposition, it is required to estimate the amount of particulate deposition from the differential pressure across the filter, but ash may accumulate in the filter wall depending on conditions, If the filter effective capacity is determined on the assumption that all ash is accumulated at the downstream closed end of the filter, there is a problem that an estimation error of the particulate accumulation amount is caused.

  The present invention has been made in view of the above problems, and provides an exhaust emission control device for an engine that can accurately estimate the amount of ash deposited that will reduce the effective filter capacity. The purpose is to improve the estimation accuracy.

  Therefore, in the present invention, while estimating the ash accumulation amount, the traveling frequency under the condition that ash is accumulated in the wall of the particulate filter is detected, and the estimated value of the ash accumulation amount is used as the traveling frequency information. It was set as the structure correct | amended based on.

  According to such a configuration, the amount of ash that accumulates at the downstream closed end of the filter and reduces the effective filter capacity from the running frequency under the condition that ash is accumulated in the wall of the particulate filter, among the entire ash amount. Therefore, it is possible to accurately determine a change in effective capacity due to ash deposition.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram of a vehicular direct injection diesel engine (hereinafter referred to as “engine”) 1 according to an embodiment of the present invention.
An air cleaner (not shown) is attached to the introduction portion of the intake passage 2 of the engine 1, and dust in the intake air is removed by this air cleaner.

A compressor section 3a of the variable nozzle turbocharger 3 is installed downstream of the air cleaner, and the intake air that has passed through the air cleaner is compressed and sent out by the compressor section 3a.
An intercooler 4 is installed downstream of the compressor unit 3a, and the intake air pumped from the compressor unit 3a is cooled by the intercooler 4.

Further, a throttle valve 6 is installed immediately before the surge tank 5, and the intake air cooled by the intercooler 4 passes through the throttle valve 6 and flows into the surge tank 5. It distributes to each cylinder through the section.
In the main body of the engine 1, the injector 7 is fixed to the approximate center of the upper part of the combustion chamber for each cylinder.

The fuel system of the engine 1 includes a common rail 8, and fuel pumped by a fuel pump (not shown) is supplied to each injector 7 via the common rail 8.
The injector 7 is operated by a fuel injection control signal from an electronic control unit (hereinafter referred to as “ECU”) 21.
The fuel injection by the injector 7 is performed in a plurality of times, and the injector 7 performs pilot injection for reducing the generated particulates in addition to the main injection for controlling the torque of the engine 1, and will be described later. Post-injection is performed to increase the exhaust temperature during regeneration of the particulate filter 12.

The pilot injection is performed with an advance angle from the main injection, and the post injection is performed with a retard angle from the main injection.
On the other hand, a turbine section 3b of the turbocharger 3 is installed in the exhaust passage 9, and a particulate filter 12 is installed downstream of the turbine section 3b for exhaust aftertreatment.

Particulates in the exhaust gas are removed from the exhaust gas when passing through the particulate filter 12.
Further, an exhaust gas recirculation pipe 10 is connected between the exhaust passage 9 and the intake air passage 2 (surge tank 5), and an exhaust gas recirculation control valve 11 is interposed in the middle of the exhaust gas recirculation pipe 10.
The exhaust gas recirculation control valve 11 is actuated by an exhaust gas recirculation control signal from the ECU 21, so that an appropriate amount of exhaust gas according to the opening degree of the exhaust gas recirculation control valve 11 is recirculated to the intake passage 2.

  The signals input to the ECU 21 include temperature sensors 31 and 32 for detecting exhaust temperatures Texhin and Texhout at the inlet and outlet of the particulate filter 12 and a pressure difference ΔPtotal across the particulate filter 12. Driven by the engine 1, an air flow meter 34 that detects the intake air flow rate of the engine 1, a crank angle sensor 35 that detects the rotation angle of the crankshaft, an accelerator opening sensor 36 that detects the depression amount of the accelerator pedal A signal from a vehicle speed sensor 37 for detecting the traveling speed of the vehicle and an exhaust pressure sensor 38 for detecting the exhaust pressure Pexh in the vicinity of the temperature sensor 31 is included.

The ECU 21 estimates the particulate accumulation amount in the particulate filter 12 based on these signals, and determines a regeneration request based on the estimation result. When it is determined that regeneration is necessary, filter regeneration control is performed to raise the exhaust gas temperature and burn the particulates under predetermined regeneration-permitted operating conditions.
Means for raising the exhaust temperature in the regeneration control include an injector 7, a turbocharger 3, an exhaust gas recirculation control valve 11 and an intake throttle valve 6. During regeneration of the filter, the main injection timing, post-injection timing of the injector 7 and By adjusting at least one of the post injection amount, the vane angle of the turbocharger 3, the opening degree of the exhaust gas recirculation control valve 11, and the opening degree of the intake throttle valve 6, the exhaust temperature is raised and the particulate filter 12 is raised. Burn the particulates deposited on the.

Here, the operation of the ECU 21 relating to the regeneration of the particulate filter 12 will be described based on the flowchart of FIG.
In step S1, it is determined whether or not the regeneration determination flag F is zero.
When it is determined that the regeneration determination flag F is 0, the process proceeds to step S2, and when it is determined that the regeneration determination flag F is not 0 (is 1), the process proceeds to step S5.

The regeneration determination flag F is set to 0 when the engine 1 is started, and is set to 1 when the regeneration of the particulate filter 12 is requested.
In step S2, the amount PM of particulates accumulated on the particulate filter 12 is estimated.
The estimation of the particulate accumulation amount PM is performed according to the flowchart of FIG.

In step S3, it is determined whether or not the particulate accumulation amount PM has reached a specified amount PM1.
When it is determined that the particulate deposition amount PM has reached the specified amount PM1, the process proceeds to step S4. When it is determined that the particulate deposition amount PM has not reached the specified amount PM1, this routine is returned.

The prescribed amount PM1 is set in advance as indicating the upper limit of the allowable accumulation amount of particulates.
In step S4, the regeneration determination flag F is set to 1.
In step S5, regeneration control for increasing the exhaust gas temperature and burning the particulates is executed.

In the regeneration control, the particulate combustion rate rPM is estimated by estimating the particulate combustion rate (indicating the amount of particulates burned per unit time) ΔPM from the exhaust gas flow rate Qexh and the temperature Tdpf of the particulate filter 12. Is calculated.
Then, in step S6, it is determined whether or not the residual rate rPM of the particulates has decreased to a specified value R1, and when the residual rate rPM has decreased to the specified value R1, the process proceeds to step S7, where the regeneration determination flag F is set to 0 and the reproduction control is terminated.

As described above, the control for regenerating the particulate filter 12 is performed, and when it is determined that the regeneration is complete (step S6), the ash deposition amount ASH is estimated according to the flowchart of FIG.
The ash refers to the unburned residue when the particulates are burned. Mainly, in addition to calcium sulfate, which is an incombustible component in the particulates, wear dust generated at the sliding portion of the engine 1, exhaust manifold Or there is rust of the turbine housing.

In the flowchart of FIG. 3, in step S <b> 21, it is determined whether or not it is immediately after the regeneration of the particulate filter 12 is completed.
If it is immediately after the completion of reproduction, the process proceeds to step S22. If it is determined that the reproduction is not immediately after completion, this routine is returned.
Immediately after the completion of regeneration, the regeneration determination flag F is set to 0, and the elapsed time or travel distance after the regeneration determination flag F is switched from 1 to 0 does not reach a predetermined value. Judge by.

In step S22, the exhaust flow rate Qexh is read.
In step S23, it is determined whether or not the read exhaust flow rate Qexh has reached a specified amount.
This determination is for confirming whether or not the differential pressure across the particulate filter 12 is a value suitable for measurement.

When it is determined that the exhaust gas flow rate Qexh has reached the specified amount, the process proceeds to step S24, and when it is determined that the exhaust gas flow rate Qexh has not reached the predetermined amount, this routine is returned.
In step S24, the filter front-rear differential pressure ΔPtotal and the travel distance D are read. The travel distance D is a travel distance that is 0 when the vehicle is shipped or when the particulate filter 12 is immediately replaced, and is calculated by accumulating the vehicle speed VSP (D = Σ (VSP × Δt): Δt is calculated. A period.)

In step S25, the ash deposition amount ASH is estimated based on the differential pressure ΔPtotal before and after the filter and the exhaust flow rate Qexh.
The estimation of the ash accumulation amount ASH is performed with reference to a map (FIG. 4) in which the ash accumulation amount ASH is assigned according to the differential pressure ΔPtotal before and after the filter and the exhaust gas flow rate Qexh.
The ash accumulation amount ASH obtained from this map is estimated as a larger value as the filter front-rear differential pressure ΔPtotal is larger under a constant exhaust flow rate Qexh, and further, ash is accumulated only at the downstream closed end of the filter. The map characteristics are set on the assumption that the amount of accumulated ash is directly reduced by the effective filter capacity.

In order to estimate the ash accumulation amount ASH more accurately, the ash accumulation amount ASH read from the map may be corrected by the filter inlet portion exhaust temperature Texhin and the exhaust pressure Pexh.
In step S26, a setting for correcting the increasing change rate of the ash deposition amount ASH with respect to the travel distance is made based on a comparison between the ash deposition amount ASH accumulated according to the travel distance so far and the ash deposition amount ASH obtained in step S25. I do.

The estimated value of the ash accumulation amount ASH with respect to the travel distance (travel history) is influenced by variations in the type of engine oil used and the oil consumption, and has an error with respect to the actual value.
Therefore, the ash accumulation amount ASH is obtained from the differential pressure ΔPtotal before and after the filter immediately after regeneration, which indicates the pressure loss due to ash alone, and the ash accumulation amount ASH indicates the actual ash accumulation amount ASH. The estimated characteristic of the ash accumulation amount ASH with respect to (travel history) is corrected so that the estimation result approaches the actual ash accumulation amount ASH.

In addition, when the amount of ash exceeding a reference | standard accumulates on the particulate filter 12, it can be set as the structure which issues the warning which urges | exchanges the particulate filter 12 with respect to a driver | operator.
In addition to the travel distance, the ash accumulation amount can be estimated from oil consumption, engine load, and the like.

FIG. 5 is a flowchart showing in detail the process of step S2 of the flowchart of FIG.
In step S201, the filter front-rear differential pressure ΔPtotal, the exhaust flow rate Qexh, and the ash deposition amount ASH are read.
The ash accumulation amount ASH is a value that is integrated based on the travel distance, and is a value that is corrected based on the differential pressure across the filter when the regeneration of the particulate filter 12 is completed.

In step S202, the pressure loss magnification k is set based on the ash accumulation amount ASH.
The ash is accumulated mainly at the downstream closed end of the particulate filter 12, and the effective capacity of the particulate filter 12 is decreased and changed by the accumulation of the ash.
Then, the differential pressure before and after the filter for the same particulate accumulation amount tends to increase as the effective capacity of the filter decreases due to the accumulation of ash, and the increase rate of the differential pressure before and after the filter due to the decrease in the effective capacity, The pressure loss magnification k is used, and by correcting the detected value of the differential pressure by the pressure loss magnification k, the pressure loss can be converted to the pressure loss at the initial capacity.

That is, when estimating the amount of particulate deposition from the differential pressure before and after the filter, the effect of ash deposition is regarded as a decrease in effective capacity, and the pressure loss generated by the effective capacity reduced by ash deposition is attributed to particulate deposition. The particulate deposition amount is estimated as being.
The correlation between the effective capacity of the filter and the pressure loss magnification k is set in advance in a map as shown in FIG. 6, and the pressure loss magnification corresponding to the effective capacity that is corrected to be reduced from the initial amount based on the ash deposition amount at that time. k is retrieved from the map.

In step S203, the pressure loss magnification k is corrected based on the ratio of the distance traveled under the condition that the ash accumulates in the filter wall in the travel distance up to that point (the travel frequency under the ash wall deposition condition).
In step S202, the pressure loss magnification k is determined on the assumption that the ash accumulation amount is all that reduces the effective capacity. However, when all of the following conditions (1) to (3) are satisfied, the ash is accumulated in the filter wall. Ash deposited in the filter walls will not reduce the effective capacity.

(1) No particulate is deposited on the particulate filter 12 (the amount deposited is less than a predetermined amount).
(2) The temperature of the particulate filter 12 is equal to or higher than a predetermined temperature.
(3) The exhaust temperature is equal to or higher than a predetermined temperature.
When the condition (1) and at least one of the conditions (2) and (3) are satisfied, it may be determined that the condition for the ash to accumulate in the filter wall is satisfied. .

In the step S203, the larger the ratio of the distance traveled under the condition that the ash is accumulated in the filter wall, in other words, the larger the ratio of the ash amount accumulated in the filter wall in the total ash accumulation amount, The pressure loss magnification k is corrected to be smaller.
That is, if all of the ash is accumulated at the downstream closed end of the filter, the ash accumulation amount is directly reduced by the effective filter capacity. However, when all of the above conditions (1) to (3) are satisfied, the ash is deposited on the filter wall. The ash deposited in the walls and deposited in the walls does not affect the reduction of the effective capacity.

Therefore, the pressure loss magnification k is corrected so as to correspond to the actual decrease in effective capacity due to the ash amount accumulated at the downstream closed end of the filter, excluding the accumulated ash amount in the wall.
In addition, instead of correcting the pressure loss magnification k based on the ratio of the distance traveled under the condition that the ash is deposited in the filter wall (running frequency under the wall deposition condition), the effective capacity or the effective capacity obtained from the ash deposition amount Even if the ash deposition amount used to determine the ash is corrected, it is substantially the same.

Further, instead of the travel distance, the ash is accumulated in the filter wall in the ratio of the oil consumed under the condition that the ash is accumulated in the filter wall in the oil consumption or the integrated value of the engine load. The pressure loss magnification k can be corrected based on the ratio of the engine load under conditions.
In step S204, the particulate accumulation amount PM is estimated based on the pressure difference ΔPtotal before and after the filter, the exhaust gas flow rate Qexh, and the pressure loss magnification k (filter effective capacity) corrected based on the running frequency under the in-wall deposition conditions. To do.

As described above, if the change in the pressure loss magnification due to the decrease in the filter effective capacity due to the ash accumulation is obtained, and the particulate accumulation amount PM is estimated from the differential pressure ΔPtotal at the reduced filter effective capacity, the ash accumulation is achieved. Therefore, even if the effective capacity of the filter greatly decreases and changes, it is possible to ensure the estimation accuracy of the particulate deposition amount PM.
Furthermore, the pressure loss magnification k is corrected based on the ratio of the distance traveled under the condition that the ash is deposited in the filter wall (running frequency under the wall deposition condition), so that the actual effective capacity can be accurately estimated and the particulate deposition. The amount estimation accuracy can be further improved.

It should be noted that there may be a so-called hysteresis characteristic in which the correlation between the differential pressure before and after and the amount of particulate deposition varies depending on whether the amount of particulate accumulation in the particulate filter 12 increases or decreases.
Therefore, in the estimation of the particulate deposition amount, it is preferable to switch the estimation characteristic of the particulate deposition amount depending on whether the particulate deposition amount is increasing or decreasing.

The block diagram of the diesel engine which concerns on embodiment. The flowchart which shows the reproduction | regeneration control routine which concerns on embodiment same as the above. The flowchart which shows the ash deposition amount estimation routine which concerns on embodiment same as the above. The diagram which shows the relationship between the exhaust flow volume Qexh and the filter front-back differential pressure (DELTA) Ptotal, and the ash deposition amount ASH in embodiment same as the above. The flowchart which shows the particulate deposition amount estimation routine which concerns on embodiment same as the above. The diagram which shows the correlation with the filter effective capacity | capacitance and pressure loss magnification in embodiment same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 2 ... Intake passage, 3 ... Turbocharger, 6 ... Intake throttle valve, 7 ... Injector, 8 ... Common rail, 9 ... Exhaust passage, 11 ... Exhaust gas recirculation control valve, 12 ... Particulate filter, 21 ... Electronic Control unit 31, 32 ... Exhaust temperature sensor, 33 ... Filter front / rear differential pressure sensor

Claims (5)

An exhaust emission control device for an engine comprising a particulate filter that collects particulates in the exhaust of a vehicle engine,
The ash accumulation amount is estimated, while the traveling frequency under the condition that ash is accumulated in the wall of the particulate filter is detected, and the estimated value of the ash accumulation amount is corrected based on the traveling frequency. Exhaust gas purification device for the engine.   Ash accumulates in the walls of the particulate filter when the amount of particulate deposition on the particulate filter is less than a predetermined amount and the temperature of the particulate filter and / or the exhaust temperature is equal to or higher than a predetermined temperature. The engine exhaust gas purification apparatus according to claim 1, wherein the exhaust gas purifying apparatus determines that the condition is satisfied.   The engine exhaust gas purification apparatus according to claim 1 or 2, wherein an effective capacity of the particulate filter is estimated based on the travel frequency and an estimated value of an ash accumulation amount.   A particulate accumulation amount on the particulate filter is estimated from an effective capacity of the particulate filter and a differential pressure before and after the particulate filter, and the regeneration request of the particulate filter is based on the particulate accumulation amount. The engine exhaust gas purification apparatus according to claim 3, wherein: The estimation of the ash accumulation amount is performed based on a travel history of the vehicle,
From the comparison of the ash accumulation amount estimated from the differential pressure across the particulate filter when the particulate accumulation amount with respect to the particulate filter is less than a predetermined amount, and the ash accumulation amount estimated from the running history of the vehicle, The engine exhaust gas purification apparatus according to any one of claims 1 to 4, wherein an estimation characteristic of an ash accumulation amount based on a travel history of the vehicle is corrected.

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