JP2015059476A - Exhaust purification system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purification system of an internal combustion engine which optimizes a fuel injection amount in forcible regeneration.SOLUTION: An exhaust purification system of an internal combustion engine includes a DOC 21 provided in an exhaust system of an engine 10; a DPF22 which is provided in a downstream side of the DOC 21 and collects PM; an electrode 27 which detects the electrostatic capacitance of the DPF 22; a DPF internal temperature calculation unit 51 which calculates an internal temperature of the DPF 22 on the basis of the electrostatic capacitance input from the electrode 27; a forcible regeneration control unit 53 which, when a PM accumulation amount in the DPF 22 reaches to a prescribed amount, carries out forcible regeneration in which fuel is injected into the DOC 21 to combust and remove particulate matters; and an injection amount correction unit 54 which corrects a fuel injection amount of the forcible regeneration control unit 53 on the basis of a temperature difference between a DPF target temperature in the forcible regeneration and the DPF internal temperature input from the DPF internal temperature calculation unit 51.

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus including a filter that collects particulate matter in exhaust gas discharged from the internal combustion engine.

  For example, a diesel particulate filter (hereinafter referred to as DPF) is known as a filter that collects particulate matter (hereinafter referred to as PM) in exhaust discharged from a diesel engine. .

  Since the DPF has a limit in the amount of collected PM, it is necessary to perform so-called forced regeneration in which accumulated PM is periodically removed by combustion. In forced regeneration, unburned hydrocarbon (HC) is supplied to an oxidation catalyst (Diesel Oxidation Catalyst: DOC) on the exhaust upstream side by oxidization by in-pipe injection or post injection, and the exhaust temperature is raised to the PM combustion temperature. Is done.

  In general, the injection amount in the exhaust pipe and the post injection amount at the time of forced regeneration are controlled based on the sensor value of an exhaust temperature sensor provided before and after the DPF (see, for example, Patent Document 1).

JP 2010-1860 A

  Incidentally, the sensor value of the exhaust temperature sensor has a problem that a response delay occurs with respect to an actual exhaust temperature change. In addition, since the exhaust temperature sensor cannot be provided inside the DPF, there is a problem that the internal temperature of the DPF cannot be accurately detected. For this reason, in the technology that performs forced regeneration based on the sensor value of the exhaust temperature sensor, there is a possibility that injection in the exhaust pipe and post injection cannot be controlled with an optimal injection amount.

  An object of the present invention is to detect the DPF internal temperature with high accuracy and to optimize the fuel injection amount during forced regeneration.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided with an oxidation catalyst provided in an exhaust system of the internal combustion engine, and an exhaust system downstream of the oxidation catalyst. A filter that collects particulate matter, a capacitance detection means that detects the capacitance of the filter, and an internal temperature of the filter is calculated based on the capacitance input from the capacitance detection means An internal temperature calculating means for performing a forced regeneration for injecting fuel to the oxidation catalyst and removing the particulate matter by combustion when a particulate matter accumulation amount of the filter exceeds a predetermined amount, and a forced regeneration Injection amount correction means for correcting the fuel injection amount of the filter regeneration means based on the temperature difference between the filter target temperature at the time and the filter internal temperature input from the internal temperature calculation means. To.

  Further, it is preferable that the injection amount correcting means corrects the fuel injection amount of the filter regeneration means with an injection correction amount necessary to bring the filter internal temperature input from the internal temperature calculating means close to the filter target temperature. .

  Further, the capacitance detection means may be composed of at least a pair of electrodes that are disposed opposite to each other with one or more partition walls in the filter to form a capacitor.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, the internal temperature of the DPF can be detected with high accuracy, and the fuel injection amount during forced regeneration can be optimized.

1 is a schematic overall configuration diagram showing an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention. It is a functional block diagram which shows ECU of this embodiment. It is a figure which shows an example of the temperature characteristic map of this embodiment. It is a figure which shows an example of the deposition amount map of this embodiment. It is a figure which shows an example of the injection quantity correction map of this embodiment. It is a flowchart which shows the control content of this embodiment. It is the figure which compared the electrostatic capacitance between electrodes, and the sensor value of an exhaust temperature sensor. It is a typical whole block diagram which shows the exhaust gas purification apparatus of the internal combustion engine which concerns on other embodiment.

  Hereinafter, an exhaust emission control device according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b.

  In the intake passage 11, an air cleaner 13, a MAF sensor 14, a compressor 15 a of the supercharger 15, an intercooler 16, an intake throttle valve 17, and the like are provided in order from the intake upstream side. In the exhaust passage 12, a turbine 15 b of the supercharger 15, an exhaust aftertreatment device 20, and the like are provided in order from the exhaust upstream side.

  The exhaust aftertreatment device 20 is configured by arranging a DOC 21 and a DPF 22 in order from the exhaust upstream side in a catalyst case 20a. An exhaust pipe injection device 23 is provided on the exhaust upstream side of the DOC 21.

  The exhaust pipe injection device 23 is a part of the filter regeneration means of the present invention, and injects unburned fuel (mainly HC) into the exhaust passage 12 in accordance with an instruction signal (pulse current) input from the ECU 50. To do. In addition, when using post injection by the multistage injection of the engine 10, this in-pipe injection device 23 may be omitted.

  The DOC 21 is formed, for example, by supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When HC is supplied by the in-pipe injection device 23 or post-injection, the DOC 21 oxidizes this and raises the exhaust temperature.

  The DPF 22 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. The DPF 22 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the amount of accumulated PM reaches a predetermined amount, so-called forced regeneration for performing combustion removal is executed. In forced regeneration, unburned fuel (HC) is supplied to the DOC 21 by the exhaust pipe injection device 23 or post injection, and the exhaust temperature flowing into the DPF 22 is raised to the PM combustion temperature (for example, about 500 to 600 ° C.). Done.

  In addition, the DPF 22 of the present embodiment is provided with a plurality of electrodes 27 that are arranged to face each other with at least one partition wall therebetween to form a capacitor. The plurality of electrodes 27 are preferable as an example of the capacitance detection means of the present invention.

  The ECU 50 performs various controls of the engine 10, the exhaust pipe injection device 23, and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like.

  Further, as shown in FIG. 2, the ECU 50 includes a DPF internal temperature calculation unit 51, a PM accumulation amount calculation unit 52, a forced regeneration control unit 53, and an injection amount correction unit 54 as some functional elements. Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

DPF internal temperature calculation unit 51 is an example of an internal temperature calculating means of the present invention, based on the electrostatic capacitance C between the electrodes 27, and calculates the internal temperature T _DPF of the DPF 22. In general, the capacitance C between the electrodes 27 is expressed by the following mathematical formula 1, where the dielectric constant ε of the medium between the electrodes 27, the area S of the electrodes 27, and the distance d between the electrodes 27.

In Formula 1, the area S and the distance d of the electrode 27 are constant, and when the dielectric constant ε changes under the influence of the exhaust temperature, the capacitance C also changes accordingly. That is, if the capacitance C between the electrodes 27 is detected, the DPF internal temperature _TDPF can be calculated. The ECU 50 stores a temperature characteristic map (see, for example, FIG. 3) indicating the relationship between the capacitance C obtained in advance through experiments or the like and the DPF internal temperature _TDPF . DPF internal temperature calculation unit 51 calculates the DPF internal temperature T _DPF by reading the corresponding value from the temperature characteristic map in the electrostatic capacitance C between the electrodes 27. Note that the DPF internal temperature T _DPF may be calculated from an approximate expression obtained in advance through experiments or the like.

The PM deposition amount calculation unit 52 calculates the PM deposition amount PM _DEP collected by the DPF 22 based on the capacitance C between the electrodes 27. In the above Equation 1, when the deposition of PM proceeds between the electrodes 27 and the dielectric constant ε and the distance d change, the capacitance C also changes accordingly. That is, if the capacitance C between the electrodes 27 is detected, the PM deposition amount PM _DEP can be calculated. The ECU 50 stores a deposition amount map (see, for example, FIG. 4) indicating the relationship between the capacitance C and the PM deposition amount PM _DEP obtained in advance through experiments or the like. The PM deposition amount calculation unit 52 calculates the PM deposition amount PM _DEP by reading a value corresponding to the capacitance C between the electrodes 27 from the deposition amount map. Note that the PM accumulation amount PM _DEP may be calculated from an approximate expression or the like obtained in advance through experiments or the like.

The forced regeneration control unit 53 is an example of the filter regeneration unit of the present invention, and controls the forced regeneration of the DPF 22 based on the PM accumulation amount PM _DEP input from the PM accumulation amount calculation unit 52. More specifically, when the PM accumulation amount PM _DEP exceeds the upper PM accumulation amount PM _MAX that can be collected in the DPF 22 (PM _DEP > PM _MAX ), the forced regeneration control unit 53 applies a predetermined amount to the in-pipe injection device 23. The forced regeneration is started by executing the exhaust pipe injection. The injection amount in the exhaust pipe at the time of this forced regeneration is corrected as necessary by an injection amount correction unit 54 described later.

The injection amount correction unit 54 performs forced regeneration based on the temperature difference ΔT between the DPF internal temperature T _DPF input from the DPF internal temperature calculation unit 51 and the target temperature T _TARGT that substantially completely burns and removes the PM in the DPF 22. Correct the fuel injection amount at the time. More specifically, the ECU 50 has an injection amount correction map (for example, see FIG. 5) showing the relationship between the temperature difference ΔT obtained in advance by experiments or the like and the injection correction amount ΔINJ necessary to compensate for the temperature difference ΔT. It is remembered. The exhaust pipe injection amount INJ _{Q_exh} during forced regeneration is obtained by reading the injection correction amount ΔINJ corresponding to the temperature difference ΔT from the injection amount correction map and adding or subtracting the read injection correction amount ΔINJ to the basic injection amount INJ _{Q_std.} It is set (INJ _{Q_exh} = INJ _{Q_std} +/- ΔINJ). The corrected fuel injection is executed by increasing or decreasing the energization pulse width of each injection applied to the injector of the in-pipe injection device 23, or by increasing or decreasing the number of injections.

  Next, based on FIG. 6, the control flow by the exhaust emission control device of the present embodiment will be described. Note that this control starts simultaneously with the ON operation of the ignition key.

In step (hereinafter, step is simply referred to as S) 100, it is determined whether or not the PM deposition amount PM _DEP acquired from the capacitance C exceeds the upper limit deposition amount PM _MAX . When the PM deposition amount PM _DEP exceeds the upper limit deposition amount PM _MAX (Yes), the process proceeds to S110 in order to start the forced regeneration of the DPF 22.

In S110, DPF internal temperature T _DPF obtained from the capacitance C and the target temperature T _TARGT are compared. If the temperature difference between the target temperature T _TARGT and DPF internal temperature T _DPF [Delta] T (absolute value) is greater than zero (Yes), the process proceeds to S120. On the other hand, when the temperature difference ΔT is zero (No), the DPF internal temperature T _DPF can be raised to the target temperature T _TARGT even if the exhaust pipe injection is executed with the basic injection amount INJ _{Q_std} . In this case, the process proceeds to S140, and the injection into the exhaust pipe is executed with the basic injection amount INJ _{Q_std} .

In S120, an injection amount correction (INJ _{Q_exh} = INJ _{Q_std} +/− ΔINJ) is performed in which the injection correction amount ΔINJ read from the injection amount correction map according to the temperature difference ΔT is added to or subtracted from the basic injection amount INJ _{Q_std.} Then, the exhaust pipe injection is executed based on the corrected exhaust pipe injection amount INJ _{Q_exh} .

In S150, it is determined whether or not the PM deposition amount PM _DEP has decreased to a lower limit threshold value PM _MIN indicating the end of regeneration of the DPF 22. If the PM accumulation amount PM _DEP has decreased to the lower threshold PM _MIN (Yes), the injection in the exhaust pipe is stopped in S160 and the present control is returned. Thereafter, each control step of S100 to S160 is repeatedly executed until the ignition key is turned off.

  Next, functions and effects of the exhaust gas purification apparatus for an internal combustion engine according to this embodiment will be described.

  As shown in FIG. 7, the capacitance C between the electrodes 27 has a characteristic that shows a quicker response than the sensor value of the exhaust temperature sensor with respect to a change in the exhaust temperature (DPF internal temperature). That is, if the capacitance C between the electrodes 27 arranged in the DPF 22 is used, the internal temperature of the DPF 22 can be detected more accurately than the sensor value of the exhaust temperature sensor provided before and after the DPF 22.

In the exhaust emission control device of the present embodiment, the injection amount in the exhaust pipe at the time of forced regeneration (or, based on the temperature difference ΔT between the DPF internal temperature T _DPF calculated from the capacitance C between the electrodes 27 and the target temperature T _TARGT The post injection amount is corrected. That is, as compared with the conventional technique based on the sensor value of the exhaust temperature sensor, the DPF internal temperature _TDPF is accurately detected, so that the exhaust pipe injection amount at the time of forced regeneration is optimized.

  Therefore, according to the exhaust emission control device of the present embodiment, the fuel injection amount at the time of forced regeneration can be accurately controlled, and the regeneration efficiency of the DPF 22 can be effectively improved. Further, it is not necessary to provide an exhaust temperature sensor before and after the DPF 22, and the cost of the entire apparatus can be effectively reduced.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, although DPF22 and DOC21 were demonstrated as what is provided separately, you may integrate these. Further, the engine 10 is not limited to a diesel engine, and can be widely applied to other internal combustion engines such as a gasoline engine.

  Further, as shown in FIG. 8, a bypass passage 25 for bypassing the DPF 22 may be connected to the exhaust passage 12, and the bypass passage 25 may be provided with a measuring DPF 22a having a small capacity. In this case, it is preferable to arrange the electrode 27 in the measurement DPF 22a and provide the bypass passage 25 with an orifice 25a (throttle) for adjusting the exhaust gas flow rate. When forced regeneration of the measurement DPF 22a is performed, a voltage may be applied to the electrode 27 to cause it to function as a heater.

10 engine 12 exhaust passage 20 exhaust aftertreatment device 21 DOC
22 DPF
23 Exhaust pipe injection device 27 Electrode 50 ECU
51 DPF internal temperature calculation unit 52 PM accumulation amount calculation unit 53 forced regeneration control unit 54 injection amount correction unit

Claims (3)

An oxidation catalyst provided in the exhaust system of the internal combustion engine;
A filter that is provided in an exhaust system downstream of the oxidation catalyst and collects particulate matter in the exhaust;
Capacitance detecting means for detecting the capacitance of the filter;
Internal temperature calculation means for calculating the internal temperature of the filter based on the capacitance input from the capacitance detection means;
Filter regeneration means for performing forced regeneration for injecting fuel to the oxidation catalyst and burning and removing particulate matter when the particulate matter accumulation amount of the filter exceeds a predetermined amount;
Injection amount correction means for correcting the fuel injection amount of the filter regeneration means based on the temperature difference between the filter target temperature during forced regeneration and the filter internal temperature input from the internal temperature calculation means. An exhaust gas purification apparatus for an internal combustion engine characterized by the above. The injection amount correction unit corrects the fuel injection amount of the filter regeneration unit with an injection correction amount necessary to bring the filter internal temperature input from the internal temperature calculation unit closer to the filter target temperature. Exhaust gas purification device for internal combustion engine. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the electrostatic capacitance detection means is configured by at least a pair of electrodes that are disposed opposite to each other with one or more partition walls in the filter to form a capacitor.

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