JP6123343B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device 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 gas discharged from a diesel engine. Yes.

  Since the DPF has a limit in the amount of collected PM, it is necessary to perform forced regeneration by periodically burning and removing the accumulated PM. Forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst upstream of the exhaust by in-pipe injection or post-injection, and raising the temperature of the exhaust gas to the PM combustion temperature by the heat generated by oxidation. Is called.

  If the fuel supply amount at the time of forced regeneration becomes larger than necessary, the DPF may be damaged due to excessive temperature rise. For this reason, based on exhaust temperature sensors provided on the exhaust upstream side and downstream side of the DPF, a technique for feedback control of the fuel supply amount during forced regeneration is also known so that the target temperature can be avoided. Yes.

JP 2010-1860 A

  By the way, the sensor value of the exhaust temperature sensor is likely to be delayed in response to a sudden change in the actual exhaust temperature. Moreover, the attachment position is upstream or downstream of the filter, and a temperature sensor cannot be installed on the filter itself. Therefore, if feedback control of the fuel supply amount during forced regeneration is performed based on the sensor value of the exhaust temperature sensor, the fuel supply amount cannot be optimally controlled especially at the start of forced regeneration, and the DPF may not be maintained at the target temperature. There is. As a result, the internal temperature of the DPF may overshoot, which may cause the DPF to melt due to excessive temperature rise.

  The present invention has been made in view of the above points, and its purpose is to improve the estimation accuracy of the internal temperature of the DPF and effectively prevent overshooting of the internal temperature of the DPF and melting of the DPF. is there.

In order to achieve the above-mentioned object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of the internal combustion engine and detects a capacitance of the filter that collects particulate matter in the exhaust gas. Based on the detected capacitance, the accumulated amount estimating means for estimating the accumulated amount of the particulate matter collected by the filter based on the detected capacitance, and the detected capacitance Te, characterized in that it comprises a filter temperature estimation means for estimating the internal temperature of the filter.

In addition, when the estimated accumulation amount reaches a predetermined threshold value, a filter regeneration unit is further provided that can perform forced regeneration by supplying fuel into the exhaust pipe and raising the temperature of the filter to the combustion temperature of the particulate matter. The filter regeneration means reduces the fuel supply amount during forced regeneration so that the estimated internal temperature is equal to or lower than the target temperature based on a target temperature that can avoid melting damage due to excessive temperature rise of the filter. Feedback control is performed, and the filter temperature estimation means estimates the internal temperature of the filter based on the accumulation amount estimated immediately before and the detected capacitance change, and the capacitance detection means In addition, the filter may include a pair of electrodes that are arranged to face each other with at least one partition wall interposed therebetween and form a capacitor.

Further, when the estimated accumulation amount reaches a predetermined threshold, fuel is supplied into the exhaust pipe, and filter regeneration means capable of performing forced regeneration to raise the temperature of the filter to the combustion temperature of the particulate matter, An exhaust gas temperature sensor that is provided at at least one of the upstream side and the downstream side of the exhaust of the filter and detects the exhaust temperature of at least one of the upstream side and the downstream side of the exhaust of the filter; Control based on the exhaust temperature detected by the exhaust temperature sensor so that the estimated internal temperature is equal to or lower than the target temperature based on the target temperature that can avoid melting damage due to excessive temperature rise of the filter To control based on the internal temperature estimated by the filter temperature estimating means, and the amount of fuel supplied during forced regeneration is feedback controlled. And, the electrostatic capacitance detecting means, disposed opposite each other across at least one or more partition walls in the filter, it may include a pair of electrodes forming a capacitor.

Further, the exhaust passage on the upstream side and the downstream side of the filter is connected to bypass the filter, and the particulate matter in the exhaust gas that is provided in the bypass passage and flows through the bypass passage. A second filter for collecting, and the pair of electrodes are disposed opposite to each other with at least one partition wall interposed between the pair of electrodes in the second filter, and forcibly regenerating the second filter. May cause the pair of electrodes to function as a heater.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is possible to improve the estimation accuracy of the internal temperature of the DPF and effectively prevent the overshoot of the internal temperature of the DPF and the melting loss of the DPF.

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 figure explaining the change of an electrostatic capacity, a DPF entrance temperature, and a DPF exit temperature in an exhaust-air-purification device of an internal-combustion engine concerning one embodiment of the present invention. 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 for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. 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. Further, in the exhaust passage 12, an exhaust pipe injection device 13, an exhaust aftertreatment device 14, a DPF inlet temperature sensor 31, and a DPF outlet temperature sensor 32 are provided in order from the exhaust upstream side.

  The exhaust pipe injection device 13 injects unburned fuel (HC) into the exhaust passage 12 in response to an instruction signal output from the ECU 20. In addition, when using the post injection by the multistage injection of the engine 10, this in-pipe injection device 13 may be omitted.

  The exhaust aftertreatment device 14 is configured by arranging an oxidation catalyst 15 and a DPF 16 in order from the exhaust upstream side in a case 14a.

  The oxidation catalyst 15 is formed by, for example, supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When the unburned fuel (HC) is supplied by the in-pipe injection device 13 or post injection, the oxidation catalyst 15 oxidizes this to raise the temperature of the exhaust gas.

  The DPF 16 is formed, for example, by arranging a large number of cells partitioned by porous ceramic partition walls along the exhaust gas flow direction, and alternately plugging the upstream side and the downstream side of these cells. . The DPF 16 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and performs so-called forced regeneration that burns and removes the PM when the PM accumulation amount reaches a predetermined amount. The forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst 15 by the exhaust pipe injection device 13 or post injection, and raising the DPF 16 to the PM combustion temperature (for example, about 600 ° C.).

  In addition, the DPF 16 of the present embodiment is provided with a pair of electrodes 17a and 17b that are disposed to face each other with at least one partition wall therebetween to form a capacitor. The pair of electrodes 17a and 17b are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20, respectively.

The DPF inlet temperature sensor 31 detects the temperature of exhaust gas flowing into the DPF 16 (hereinafter referred to as inlet temperature T _IN ). The DPF outlet temperature sensor 32 detects the temperature of exhaust gas flowing out from the DPF 16 (hereinafter referred to as outlet temperature T _OUT ). The inlet temperature T _IN and the outlet temperature T _OUT are output to the electrically connected ECU 20.

  The ECU 20 performs various controls such as fuel injection of the engine 10 and the exhaust pipe injection device 13, and includes a known CPU, ROM, RAM, input port, output port, and the like. In addition, the ECU 20 includes a capacitance calculation unit 21, a PM accumulation amount estimation unit 22, a DPF temperature estimation unit 23, and a regeneration control unit 24 as some functional elements. Each of these functional elements will be described as being included in the ECU 20 which is an integral hardware, but any one of these may be provided in separate hardware.

  In the present embodiment, the capacitance calculation unit 21 and the pair of electrodes 17a and 17b constitute the capacitance detection means of the present invention, and the PM accumulation amount estimation unit 22, the DPF inlet temperature sensor 31, and the DPF outlet temperature. The sensor 32 constitutes the PM accumulation amount estimation means of the present invention, and the regeneration control unit 24 and the exhaust pipe injection device 13 (or the fuel injection device (not shown) of the engine 10) constitute the filter regeneration means of the present invention. .

  The capacitance calculating unit 21 calculates the PM deposition amount from the capacitance C between the electrodes 17a and 17b based on signals input from the pair of electrodes 17a and 17b. Capacitance C is determined by PM deposition based on the relationship of Equation 1 below, which is the dielectric constant ε of the medium between the electrodes 17a and 17b, the area S of the electrodes 17a and 17b, and the distance d between the electrodes 17a and 17b. It changes as the dielectric constant ε and the distance d change.

The PM accumulation amount estimation unit 22 calculates the average value T _{AVE of the} inlet temperature T _IN detected by the DPF inlet temperature sensor 31 and the outlet temperature T _OUT detected by the DPF outlet temperature sensor 32, and is calculated by the capacitance calculation unit 21. The PM deposition amount PM _DEP collected in the DPF 16 is estimated on the basis of the capacitance C to be generated. For the estimation of the PM deposition amount PM _DEP , an approximate expression or a map obtained in advance by experiments can be used.

The DPF temperature estimation unit 23 estimates the internal temperature of the DPF 16 (hereinafter, DPF internal temperature T _DPF ). As shown in FIG. 2, the change in the capacitance C shows the same responsiveness as the detection values of the DPF inlet temperature sensor 31 and the DPF outlet temperature sensor 32. Further, the change in the capacitance C shows faster response than the DPF inlet temperature sensor 31 and the DPF outlet temperature sensor 32. The DPF temperature estimation unit 23 of the present embodiment calculates the DPF internal temperature T _DPF based on the capacitance C calculated by the capacitance calculation unit 21 and the PM deposition amount PM _DEP estimated by the PM deposition amount estimation unit 22. presume.

More specifically, the PM deposition amount changes depending on the operation state, but there is a limit to change in a predetermined short time (for example, about 1 second). In this embodiment, the PM deposition amount PM _DEP estimated immediately before is treated as a fixed value, and the DPF internal temperature T _{DPF that} cannot be followed by the DPF inlet temperature sensor 31 or the DPF outlet temperature sensor 32 due to the instantaneous change in the capacitance C. The sudden temperature change of is estimated. For the estimation of the DPF internal temperature _TDPF , an approximate expression or a map obtained in advance by experiments can be used.

When the PM accumulation amount PM _DEP estimated by the PM accumulation amount estimation unit 22 reaches the upper limit accumulation amount PM _MAX of PM that can be collected in the DPF 16, the regeneration control unit 24 injects fuel into the in-pipe injection device 13 ( (Or, post injection) is performed.

The reproduction control unit 24, the fuel injection amount at the time of forced regeneration is feedback controlled based on a change in the DPF internal temperature T _DPF estimated by DPF temperature estimation unit 23. More specifically, the ECU 20 stores in advance a target temperature T _TAR that can avoid melting damage due to excessive temperature rise of the DPF 16. The regeneration control unit 24 feedback-controls the fuel injection amount by the in-pipe injection device 13 (or post injection) so that the DPF internal temperature T _DPF estimated by the DPF temperature estimation unit 23 is equal to or lower than the target temperature T _TAR. . Thereby, the overshoot of the internal temperature of the DPF 16 due to the rapid combustion of the accumulated PM is avoided, and the DPF 16 can be effectively prevented from being damaged. At this time, the control for opening the EGR valve 40 or closing the intake throttle valve 41 is performed alone or in combination, and the control for lowering the exhaust oxygen concentration is performed alone or in combination with the fuel injection amount feedback control described above. You may go.

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

  In the conventional exhaust purification apparatus, the fuel supply amount at the time of forced regeneration is feedback controlled based on the sensor value of the exhaust temperature sensor that detects the inlet temperature and outlet temperature of the DPF. However, since the exhaust temperature sensor is slower in response than the capacitance C (see FIG. 2), the feedback control based on the exhaust temperature sensor cannot detect signs of abnormal combustion of the collected PM, and the fuel injection amount Since it cannot be reflected in the control, the fuel supply amount cannot be optimally controlled particularly at the start of forced regeneration, and the DPF may not be maintained at the target temperature. As a result, the internal temperature of the DPF may overshoot, which may cause the DPF to melt due to excessive temperature rise. In order to avoid this, it is necessary to perform forced regeneration with a light PM trapping amount at which abnormal combustion cannot surely occur, which shortens the regeneration interval and leads to deterioration of fuel consumption.

  On the other hand, the exhaust purification apparatus of this embodiment performs feedback control of the fuel supply amount at the time of forced regeneration by estimating the internal temperature of the DPF 16 from the change in the capacitance C, which is faster in response than the exhaust temperature sensor. ing. That is, the internal temperature of the DPF 16 is estimated with high accuracy on the basis of the change in the capacitance C that shows a quick response from the start of forced regeneration compared to the exhaust temperature sensor, and the internal temperature of the DPF 16 is maintained at the target temperature. As described above, the fuel supply amount is optimized.

  Therefore, according to the exhaust gas purification apparatus of the present embodiment, overshooting of the internal temperature of the DPF 16 during forced regeneration is effectively prevented, and it is possible to reliably prevent melting of the DPF 16 due to excessive temperature rise. Further, the fuel supply amount at the time of forced regeneration is optimized, and the fuel efficiency can be effectively improved.

  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, as shown in FIG. 3, a bypass passage 18 that bypasses the DPF 16 may be connected to the exhaust passage 12, and the bypass passage 18 may include a measurement DPF 16 a (second filter) having a small capacity. In this case, it is preferable that the pair of electrodes 17a and 17b are arranged opposite to each other with at least one partition wall in the measurement DPF 16a, and an orifice 18a (throttle) for adjusting the flow rate of the exhaust gas is provided in the bypass passage 18. . Further, when the forced regeneration of the measurement DPF 16a is executed, a voltage may be applied to the pair of electrodes 17a and 17b so as to function as a heater.

DESCRIPTION OF SYMBOLS 10 Engine 12 Exhaust passage 13 Exhaust pipe injection apparatus 14 Exhaust after-treatment apparatus 15 Oxidation catalyst 16 DPF (filter)
20 ECU
DESCRIPTION OF SYMBOLS 21 Capacitance calculating part 22 PM deposition amount estimation part 23 DPF temperature estimation part 24 Reproduction | regeneration control part 31 Inlet temperature sensor 32 Outlet temperature sensor 40 RGR valve 41 Intake throttle valve

Claims (4)

A filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
Capacitance detecting means for detecting the capacitance of the filter;
A deposition amount estimating means for estimating a deposition amount of the particulate matter collected by the filter based on the detected capacitance;
Filter temperature estimation means for estimating an internal temperature of the filter based on the detected capacitance;
Exhaust purification system of an internal combustion engine, characterized in that it comprises a. When the estimated amount of deposition reaches a predetermined threshold, the filter further comprises filter regeneration means capable of performing forced regeneration by supplying fuel into the exhaust pipe and raising the temperature of the filter to the combustion temperature of the particulate matter,
The filter regeneration means feeds back the fuel supply amount during forced regeneration so that the estimated internal temperature is equal to or lower than the target temperature based on a target temperature that can avoid melting damage due to excessive temperature rise of the filter. Control
The filter temperature estimation means estimates the internal temperature of the filter based on the deposition amount estimated immediately before and the detected change in capacitance,
2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the capacitance detection means includes a pair of electrodes that are disposed opposite to each other with at least one partition wall in the filter and that form a capacitor. Filter regeneration means capable of performing forced regeneration by supplying fuel into the exhaust pipe and raising the temperature of the filter to the combustion temperature of the particulate matter when the estimated accumulation amount reaches a predetermined threshold;
An exhaust temperature sensor provided at at least one of the upstream side and the downstream side of the exhaust of the filter to detect the exhaust temperature of at least one of the upstream side and the downstream side of the exhaust of the filter;
Further comprising
The filter regeneration means is detected by the exhaust temperature sensor so that the estimated internal temperature is equal to or lower than the target temperature based on a target temperature that can avoid melting damage due to excessive temperature rise of the filter. Switching from control based on the exhaust temperature to control based on the internal temperature estimated by the filter temperature estimation means, feedback control of the fuel supply amount during forced regeneration,
The electrostatic capacitance detecting means, wherein disposed facing each other across at least one or more partition walls in the filter, the exhaust purification system of an internal combustion engine according to claim 1 including a pair of electrodes forming a capacitor. A bypass passage that bypasses the filter by connecting the exhaust passage upstream and downstream of the filter;
A second filter that is provided in the bypass passage and collects particulate matter in the exhaust gas flowing through the bypass passage;
The pair of electrodes are disposed opposite to each other with at least one or more partition walls in the second filter,
The exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3 , wherein when the forced regeneration of the second filter is executed, the pair of electrodes function as a heater.

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