JP5136465B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that includes a filter that collects PM (Particulate Matter) contained in exhaust gas of an internal combustion engine such as an automobile diesel engine.

  In recent years, internal combustion engines mounted on automobiles and the like have been required to reduce exhaust emissions. In particular, compression ignition type diesel engines using light oil as fuel, in addition to CO, HC and NOx, It is necessary to remove exhaust particulates such as (Soot) and SOF (Solvable Organic Fraction). For this reason, a particulate filter is disposed in the exhaust passage, where exhaust particulates in the exhaust gas are collected.

  The particulate filter allows the inflowing exhaust gas to permeate through the porous partition walls, and at that time, collects exhaust particulates in the exhaust gas through the surfaces and pores of the partition walls. If the amount collected and accumulated excessively increases, the back pressure of the internal combustion engine increases due to an increase in flow resistance in the particulate filter, resulting in a decrease in output. For this reason, it is necessary to regenerate the particulate filter by appropriately removing the exhaust particulates deposited on the particulate filter from the particulate filter and recovering the exhaust gas flow ability of the particulate filter. Such regeneration of the particulate filter is generally called “PM regeneration”.

  PM regeneration is made possible during operation of the internal combustion engine. An oxidation catalyst such as platinum is provided in the particulate filter, and fuel is supplied to the particulate filter by post injection for injecting fuel in the exhaust stroke. Is used to oxidize and remove the deposited exhaust particulates that are difficult to oxidize compared to the injected fuel.

  If PM regeneration is performed frequently, the fuel consumption deteriorates. On the other hand, if there is too much time until the next PM regeneration, the accumulated amount of exhaust particulates will be excessive, and the accumulated exhaust particulates will burn rapidly in the PM regeneration process. The curate filter becomes extremely hot and may be damaged. For this reason, it is desirable to determine the PM regeneration timing by judging the accumulation state of the exhaust particulates.

  In Patent Documents 1 and 2, etc., this is utilized by utilizing the fact that the differential pressure between the inlet and outlet of the particulate filter increases due to the increase in the flow resistance due to the increase in the amount of exhaust particulates deposited on the particulate filter. A technique is disclosed that detects a differential pressure, and determines that it is time to regenerate PM when the detected differential pressure exceeds a predetermined value.

  The technique for determining the accumulation state of exhaust particulates based on this differential pressure utilizes the fact that the exhaust gas flow state in the particulate filter changes according to the accumulation state of exhaust particulates. Even so, if the flow state of the exhaust gas in the particulate filter is different, the known deposition state also varies. For this reason, there is a possibility that the regeneration time of the particulate filter is delayed or the PM regeneration frequency is increased.

  Therefore, Patent Document 3 proposes an exhaust gas purification apparatus for an internal combustion engine that can accurately determine the accumulation state of exhaust particulates in consideration of the exhaust gas flow state in the particulate filter.

  In the technology described in Patent Document 3, an ECU (Electronic Control Unit) is used in an exhaust gas purification apparatus that determines a PM accumulation state based on a differential pressure of a DPF (Diesel Particulate Filter) detected by a differential pressure sensor. When the uniformity of the temperature distribution in the DPF is low, the judgment of the PM accumulation state based on the differential pressure is prohibited. The uniformity of the temperature distribution of the DPF is based on the temperature of the inlet detected by the exhaust temperature sensor provided immediately upstream of the DPF, and the temperature in the DPF is estimated at a position away from the inlet in the exhaust gas flow direction. Judgment is made based on the temperature range of a plurality of parts.

JP 2003-27919 A JP 2003-83035 A JP 2005-226633 A

  At present, the center temperature of the DPF is estimated by using a model based on the amount of heat of entering gas, the amount of heat of PM oxidation, the amount of reaction heat of added fuel, and the amount of heat of reaction of exhaust gas.

  Since only the central temperature in the DPF is estimated in this way, the temperature other than the central portion in the DPF is not known, and the temperature distribution varies depending on the driving conditions, so that each temperature has an SML (Soot Mass). It is necessary to set the target temperature at the time of PM regeneration with a margin from (Limit), and the interval until PM regeneration becomes longer accordingly. As a result, exhaust heat and fuel consumption due to PM regeneration may be seriously deteriorated. This is because the temperature distribution in the DPF is not estimated.

  The present invention has been made in view of such a background, and an object thereof is to provide an exhaust emission control device for an internal combustion engine that can predict and prevent local thermal runaway of a particulate filter.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is an exhaust gas purification apparatus for an internal combustion engine provided with a DPF in an exhaust passage, and the internal state of the particulate filter is changed from the state in the particulate filter. Estimating means for estimating the temperature distribution from the exhaust gas flow rate, DPF differential pressure, center temperature before and after DPF, soot distribution in the DPF, exhaust gas calorific value, fuel heating value for heating, and DPF heat radiation amount , Based on the temperature distribution in the particulate filter, a calculating means for calculating a temperature gradient in the particulate filter, and whether the temperature gradient in the particulate filter calculated by the calculating means is greater than or equal to a set value and discriminating means for discriminating whether the temperature gradient in said particulate filter set by discrimination means When it is determined to exceed the lower the target temperature during PM regeneration, and a PM continuation means for continuing the PM elimination control based on the target temperature.

  According to the above configuration, the temperature distribution in the particulate filter is estimated from the state in the particulate filter, and the temperature gradient in the particulate filter is calculated based on the estimated temperature distribution in the particulate filter. The When the temperature gradient in the particulate filter is calculated, it is determined whether or not the calculated temperature gradient in the particulate filter exceeds a set value. As a result of this determination, when the temperature distribution in the particulate filter exceeds the set value, the target temperature during PM regeneration is lowered, and PM regeneration is continued based on this target temperature. Thus, by considering the local temperature distribution in the particulate filter, local thermal runaway of the particulate filter can be predicted and prevented. Therefore, SML improves. By improving this SML, the interval until PM regeneration can be lengthened, and deterioration of exhaust gas and fuel consumption can be prevented by PM regeneration.

  Here, the “state in the particulate filter” includes the exhaust gas flow rate, the particulate filter differential pressure, the particulate filter center temperature, the particulate filter A / F (air-fuel ratio), and the particulate filter soot distribution. Exhaust gas heat generation amount, temperature rising fuel heat generation amount, particulate filter heat dissipation amount, and the like can be exemplified.

  According to the present invention, it is possible to provide an exhaust gas purification device for an internal combustion engine that can predict and prevent local thermal runaway of the particulate filter.

1 is a schematic configuration diagram showing a diesel engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied. It is a flowchart which shows the flow of control of the exhaust gas purification device of an internal combustion engine.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Configuration>
FIG. 1 is a schematic configuration diagram showing a diesel engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied.

  As shown in FIG. 1, an internal combustion engine (hereinafter referred to as “engine”) 1 includes an in-line four-cylinder mainly composed of a fuel supply system 2, a combustion chamber 3, an intake system 6 and an exhaust system 7. The diesel engine system.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, a fuel injection valve 23, a cutoff valve 24, a fuel addition nozzle 26, an engine fuel passage 27, an addition fuel passage 28, and the like.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and then supplies it to the common rail 22 via the engine fuel passage 27.

  The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 23.

  The fuel injection valve 23 includes an electromagnetic solenoid therein, and is appropriately opened to inject and supply fuel into the combustion chamber 3.

  The supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition nozzle 26 via the addition fuel passage 28.

  The added fuel passage 28 is provided with the shutoff valve 24 for shutting off the added fuel passage 28 and stopping fuel addition in an emergency.

  The fuel addition nozzle 26 is configured so that the fuel addition amount to the exhaust system becomes a target addition amount (addition amount at which the exhaust A / F becomes the target A / F) by an addition control operation by the ECU 4 described later. The valve opening timing is controlled by an electronically controlled on / off valve so that the addition timing becomes a predetermined timing. That is, a desired fuel is injected and supplied from the fuel addition nozzle 26 to the exhaust system 7 (from the exhaust port 71 to the exhaust manifold 72) at an appropriate timing.

  The intake system 6 includes an intake manifold 63 connected to an intake port formed in the cylinder head, and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. In addition, an air cleaner 65, an air flow meter 43, and a throttle valve 62 are disposed in this intake passage in order from the upstream side.

  The air flow meter 43 outputs an electrical signal corresponding to the amount of air flowing into the intake passage via the air cleaner 65.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. Further, a maniverter 77 including a NOx storage catalyst (hereinafter referred to as “NSR (NOx Storage Reduction) catalyst”) 75 and a DPF 76 is disposed in the exhaust passage. The NSR catalyst 75 is an NOx storage reduction catalyst and has a conventionally known structure. The DPF 76 is a filter that functions as a PM trapping device, and has a conventionally known structure.

  Further, the engine 1 is provided with a turbocharger 5. The turbocharger 5 includes a turbine wheel 5B and a compressor wheel 5C that are connected via a turbine shaft 5A. The compressor wheel 5C is disposed facing the inside of the intake pipe 64, and the turbine wheel 5B is disposed facing the inside of the exhaust pipe 73. For this reason, the turbocharger 5 performs a so-called supercharging operation in which the compressor wheel 5C is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 5B to increase the intake pressure.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5. The throttle valve 62 provided further downstream than the intercooler 61 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly. It has a function of narrowing down the area and adjusting (reducing) the supply amount of the intake air.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. The EGR passage 8 is opened and closed steplessly by electronic control, and the exhaust gas passing through the EGR passage 8 (recirculating) is cooled by an EGR valve 81 that can freely adjust the flow rate of exhaust gas flowing through the passage. An EGR cooler 82 is provided.

  Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output. For example, the rail pressure sensor 41 outputs a detection signal corresponding to the pressure of the fuel stored in the common rail 22. The fuel pressure sensor 42 outputs a detection signal corresponding to the pressure (fuel pressure) of the fuel flowing through the added fuel passage 28. The air flow meter 43 outputs a detection signal corresponding to the flow rate (intake amount) of intake air upstream of the throttle valve 62 in the intake system 6. The A / F sensor 44 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas downstream of the catalyst casing of the exhaust system 7. Similarly, the exhaust temperature sensor 45 outputs a detection signal corresponding to the temperature of the exhaust gas downstream of the catalyst casing of the exhaust system 7. The accelerator opening sensor 46 is attached to the accelerator pedal and outputs a detection signal corresponding to the amount of depression of the pedal. The crank angle sensor 47 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. The intake pressure sensor 48 is provided in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The intake air temperature sensor 49 is provided in the intake manifold 63 and outputs a detection signal corresponding to the intake air temperature. These sensors 41 to 49 are electrically connected to the ECU 4.

  Although not particularly shown, the ECU 4 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup RAM, a timer, a counter, and the like, and an A / D (Analog / An external input circuit including a digital converter and an external output circuit are connected by a bidirectional bus.

  The ECU 4 configured as described above inputs detection signals of the various sensors via an external input circuit, performs basic control on fuel injection and the like of the engine 1 based on these signals, and outputs from the fuel addition nozzle 26. Various controls relating to the operating state of the engine 1 are executed, such as fuel addition control relating to the addition timing and addition amount for fuel addition.

  Further, the ECU 4 acquires the differential pressure across the DPF 76 (DPF differential pressure) when PM is collected in the DPF 76. Specifically, a pre-DPF pressure detection pipe 76a is provided in a gap on the upstream side (engine 1 side) of the DPF 76 for removing PM of exhaust gas, and a post-DFF pressure detection pipe 76b is provided on the downstream side of the DPF 76. The pre-DFF pressure detection pipe 76a and the post-DFF pressure detection pipe 76b are connected to a differential pressure transducer 78 that detects the differential pressure (DPF differential). The DPF differential pressure detected by the differential pressure transducer 78 is input to the ECU 4.

  Further, the ECU 4 acquires the center temperature before and after the DPF 76. Specifically, DPF temperature sensors 101 and 102 are provided before and after the DPF 76 (upstream and downstream). The first DPF temperature sensor 101 provided on the front side (upstream side) of the DPF detects the center temperature on the front side of the DPF 76, and the detected front center temperature of the DPF 76 is input to the ECU 4. On the other hand, the second DPF temperature sensor 102 provided on the rear side (downstream side) of the DPF detects the center temperature on the rear side of the DPF 76, and the detected rear center temperature on the DPF 76 is input to the ECU 4.

  Furthermore, the ECU 4 acquires the outside air temperature. Therefore, the outside air temperature detected by the outside air temperature sensor 103 is input to the ECU 4.

<Control flow>
FIG. 2 is a flowchart showing a control flow of the exhaust gas purification apparatus for the internal combustion engine.

  Referring to FIG. 2, when PM regeneration is started, ECU 4 determines whether or not the temperature gradient in DPF 76 exceeds danger value α (DPF temperature gradient (X, Y, Z)> danger value α). Is determined (step S1).

  In this step S1, in calculating the temperature gradient in the DPF 76 (DPF temperature gradient (X, Y, Z)), the ECU 4 first calculates the temperature distribution in the DPF 76 (DPF temperature (DPF temperature (X X, Y, Z)) is estimated.

DPF temperature (X, Y, Z) = func. (A, B, C, D, E, F, G) (1)
However, A: exhaust gas flow rate, B: DPF differential pressure, C: center temperature before and after DPF, D: soot distribution in DPF, E: exhaust gas calorific value, F: fuel heating value for temperature increase, G: DPF heat radiation amount . Exhaust gas amount of (A), func. (B) DPF differential pressure, func. (C) Center temperature before and after DPF, func. (D) Soot distribution in DPF, func. (E) Exhaust gas calorific value, func. (F) The temperature rise fuel heating value and func. The DPF heat release amount of (G) is obtained as follows, for example.

  func. The exhaust gas amount (A) is obtained from the detection signal of the air flow meter 43 input to the ECU 4. func. The DPF differential pressure in (B) is obtained from the detection signal of the differential pressure transducer 78 input to the ECU 4. func. The center temperature before and after the DPF in (C) is obtained from the detection signals of the DPF temperature sensors 101 and 102 input to the ECU 4. func. The exhaust gas heat quantity of (E) is obtained by the ECU 4 estimating the exhaust gas concentration and the temperature in each part of the DPF. func. The temperature rise fuel heating amount (F) is obtained by the ECU 4 estimating the temperature rise fuel amount and the temperature in each part of the DPF. func. The amount of DPF heat release in (G) is obtained by the ECU 4 estimating the temperature in each part of the DPF and the outside air temperature (detection signal from the outside air temperature sensor 103).

  Here, “the temperature of each part in the DPF” is obtained using the previous DPF temperature (X, Y, Z) stored as a history in the ECU 4.

Also, func. The (D) soot distribution in the DPF is obtained based on the following equation (2).
Soot deposition amount (X, Y, Z) = H + func. (A, B, I, J, K) -L (2)
However, H: last soot accumulation amount (X, Y, Z), I: DPF temperature (X, Y, Z), J: A / F in DPF, K: engine exhaust soot amount), L: Soot oxidation rate (X, Y, Z)
The func. (I) DPF temperature (X, Y, Z), func. (J) DPFA / F, func. (K) engine discharge soot amount, and func. (L) is obtained, for example, as follows.

  func. The DPF temperature (X, Y, Z) of (I) is obtained using the previous DPF temperature (X, Y, Z) stored as a history in the ECU 4. func. The A / F in the DPF (J) is obtained from the detection signal of the A / F sensor 44 input to the ECU 4. func. The engine discharge soot amount (K) is obtained by calculation using the map and the correction amount in the ECU 4.

  Also, func. The soot oxidation rate (X, Y, Z) of (L) is obtained based on the following equation (3).

Soot oxidation rate (X, Y, Z) = func. (A, B, I, J, H) (3)
The func. The function factors (A) to (L) may be obtained by map calculation in the ECU 4.

When the temperature distribution in the DPF 76 (DPF temperature (X, Y, Z)) is estimated as described above, the ECU 4 calculates the temperature gradient in the DPF 76 (DPF temperature gradient (X , Y, Z)).
(DPF temperature gradient (X, Y, Z) =
DPF temperature (Xn, Ym, Zl)-DPF temperature (X, Y, Z) (4) As described above, the temperature gradient in the DPF 76 (DPF temperature gradient (X, Y, Z)) ) Is calculated, the ECU 4 compares the calculated DPF temperature gradient (X, Y, Z) with the danger value α. As a result of this comparison, if the DPF temperature gradient (X, Y, Z) exceeds the danger value α, the ECU 4 lowers the target temperature during PM regeneration control (step S2), and based on this target temperature. PM regeneration is continued (step S3). On the other hand, if the DPF temperature gradient (X, Y, Z) is equal to or less than the dangerous value α, the ECU 4 jumps control to step S3 and continues PM regeneration without lowering the target temperature.

  These series of controls are repeatedly executed until the engine 1 is stopped.

<Action and effect>
The temperature distribution in the DPF 76 is estimated from the exhaust gas flow rate, the DPF differential pressure, the center temperature before and after the DPF, the A / F in the DPF, the soot distribution in the DPF, the heat generation amount of the exhaust gas, the heating heat generation amount, and the DPF heat dissipation amount. Based on the estimated temperature distribution in the DPF 46, a temperature gradient in the DPF 76 (DPF temperature gradient (X, Y, Z)) is calculated. When the temperature gradient in the DPF 76 (DPF temperature gradient (X, Y, Z)) is calculated, the calculated temperature gradient in the DPF 76 (DPF temperature gradient (X, Y, Z)) exceeds the danger value α. It is determined whether or not. As a result of this determination, if the temperature distribution in the DPF 76 (DPF temperature gradient (X, Y, Z)) exceeds the dangerous value α, the target temperature during PM regeneration is lowered, and PM based on this target temperature. Playback continues.

  Thus, by considering the local temperature distribution in the DPF 76, local thermal runaway of the DPF 76 can be predicted and prevented. Therefore, SML improves. By improving this SML, the interval until PM regeneration can be lengthened, and deterioration of exhaust gas and fuel consumption can be prevented by PM regeneration.

  The present invention is not limited to the above embodiment.

  For example, in the above-described embodiment, the example in which the DPF is used as the particulate filter has been described. However, the present invention is not limited to such a configuration. Even when DPNR (Diesel Particle-NOx Reduction) is used as the particulate filter, the object of the present invention can be sufficiently achieved.

  In addition, it goes without saying that various design changes and modifications can be made within the scope of the claims attached to this specification.

1 engine (internal combustion engine)
43 Air Flow Meter 44 A / F Sensor 76 DPF
78 Differential pressure transducer 101, 102 DPF temperature sensor 103 Outside air temperature sensor

Claims (1)

An exhaust gas purification apparatus for an internal combustion engine provided with a particulate filter in an exhaust passage,
Based on the state in the particulate filter, the temperature distribution in the particulate filter is defined as the exhaust gas flow rate, the DPF differential pressure, the center temperature before and after the DPF, the soot distribution in the DPF, the exhaust gas calorific value, the heating fuel heating value and the DPF. An estimation means for estimating from the heat dissipation amount ;
Calculation means for calculating a temperature gradient in the particulate filter based on the temperature distribution in the particulate filter estimated by the estimation means;
Determining means for determining whether or not the temperature gradient in the particulate filter calculated by the calculating means is greater than or equal to a set value;
When it is determined by the determination means that the temperature gradient in the particulate filter exceeds the set value, the target temperature during PM regeneration is lowered, and PM regeneration is continued to continue PM regeneration based on this target temperature And an exhaust emission control device for an internal combustion engine.

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