JP2012012983A - Diesel particulate filter system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel particulate filter system which has a simple structure, can widely raise a temperature, and can detect a PM quantity.SOLUTION: The diesel particulate filter system includes: a porous filter body 2 consisting of a silicon carbide to collect PM; two electrodes 3 and 4 in contact with a circumference of the filter body 2 and opposed mutually; a detecting circuit 5 for detecting the PM quantity accumulated in the filter body 2 based on the change of a reply signal when an AC current is applied between the two electrodes 3 and 4; and a temperature raising circuit 6 for incinerating the PM accumulated in the filter body 2 by applying a DC current between the two electrodes 3 and 4 to raise the temperature of the filter body 2.

Description

  The present invention relates to a diesel particulate filter that purifies exhaust gas from an engine, and relates to a diesel particulate filter system that has a simple structure, can raise temperature over a wide range, and can detect the amount of PM.

  In vehicles equipped with engines such as diesel engines, a diesel particulate filter (DPF) is installed in the exhaust pipe of the engine to collect particulate matter (particurate matter) contained in the exhaust gas. ing. The DPF is a member that temporarily collects PM, having a honeycomb pore structure (or a square pore structure) made of cordierite, silicon carbide (SiC), or the like.

  When a large amount of PM trapped in the DPF accumulates, the exhaust pressure of the engine rises and the engine characteristics deteriorate. Therefore, it is necessary to burn and remove the accumulated PM by raising the temperature of the DPF. This operation is called DPF regeneration.

JP-A-6-323129 JP 2000-297625 A JP 2002-213230 A

  As means for regenerating DPF, the DPF is heated by raising the exhaust temperature by fuel injection, the burner is provided upstream of the DPF and the DPF is heated by the burner's thermal power, and the DPF has a built-in electric heater. There is an electric heater that raises the temperature of the DPF.

However, when fuel injection or burner combustion is performed, the amount of fuel consumed increases and the amount of CO ₂ emitted increases. Therefore, it is preferable to raise the DPF temperature with an electric heater from the viewpoints of economy and environmental protection. However, when the electric heater is composed of a heating wire, the structure for incorporating the heating wire inside the DPF is complicated, the temperature in the immediate vicinity of the heating wire is raised, and the entire DPF cannot be heated in a wide range, Issues such as the need for electric power remain.

  On the other hand, as means for determining the DPF regeneration timing, the DPF regeneration timing is used every time the travel distance of the vehicle reaches a predetermined value, and the difference (differential pressure) between the exhaust gas pressure upstream and downstream of the DPF reaches the threshold value. Then, there are things that make the DPF regeneration time. However, the DPF regeneration timing is determined from the travel distance of the vehicle or from the differential pressure because it is difficult to detect the PM amount. When the DPF regeneration timing is determined by these means, the threshold value is set so that the DPF regeneration is performed early before the PM amount becomes too large, so the DPF regeneration is performed more frequently than necessary. As a result, energy is wasted regardless of the DPF regeneration means.

  Accordingly, an object of the present invention is to provide a diesel particulate filter system that solves the above problems, has a simple structure, can raise the temperature over a wide range, and can detect the amount of PM.

  In order to achieve the above object, the present invention provides a porous filter body made of silicon carbide for collecting particulate matter, two electrodes in contact with the outer periphery of the filter body and facing each other, and the two A detection circuit for detecting the amount of particulate matter accumulated in the filter body based on a change in response signal when an alternating current is applied between the electrodes, and a direct current between the two electrodes to apply the filter A temperature raising circuit for incinerating the particulate matter accumulated in the filter body by raising the temperature of the body.

  The temperature raising circuit may convert the regenerative current of the retarder into a direct current and apply it between the two electrodes.

  The present invention exhibits the following excellent effects.

  (1) The structure is simple.

  (2) A wide range of temperature increases can be achieved.

  (3) The PM amount can be detected.

It is a block block diagram of the DPF system which shows one Embodiment of this invention. It is a block diagram of the exhaust pipe to which this invention is applied. It is an equivalent circuit diagram for demonstrating the principle of PM amount detection.

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

  As shown in FIG. 1, a DPF system 1 according to the present invention includes a porous filter body 2 made of silicon carbide for collecting PM, and two electrodes that are in contact with the outer periphery of the filter body 2 and face each other. 3 and 4, and a detection circuit 5 for detecting the amount of PM accumulated in the filter body 2 based on a change in response signal when an alternating current is applied between the two electrodes 3 and 4, and the two electrodes 3 and 4 A heating circuit 6 is provided for incinerating PM accumulated in the filter body 2 by applying a direct current therebetween to raise the temperature of the filter body 2.

  The structure of the filter body 2 may be the same as a conventional structure. The material of the filter body 2 is preferably silicon carbide through which a current flows well in order to use the filter body 2 itself as an electric heater (see Patent Documents 1 to 3).

  The electrodes 3 and 4 are arranged above and below the filter body 2 so as to face each other with the filter body 2 interposed therebetween. The electrodes 3 and 4 are planar electrodes that are in close contact with the upper and lower surfaces of the filter body 2 so that current flows in a wide range without being biased in the filter body 2.

  The detection circuit 5 includes a power source / detection unit 7 including an AC power source (high frequency oscillator) that generates an AC current having one or more frequencies and a circuit that electrically detects a change in capacitance of the load, AC superposition, and DC. And an AC coupling capacitor 8 for blocking.

  The temperature raising circuit 6 is composed of a DC power source, and an AC coupling capacitor 8 is connected in the middle of the wiring connecting the temperature raising circuit 6 and the electrode 3. An inductor for AC interruption may be inserted closer to the temperature rising circuit 6 side than the connection point 9 between the AC coupling capacitor 8 and the temperature rising circuit 6.

  As shown in FIG. 2, in a vehicle to which the present invention is applied, a DPF 23 is installed in an exhaust pipe 22 connected to an engine 21. Although the inside of the DPF 23 is not shown, the DPF 23 is one in which the filter main body 2 of FIG. 1 is accommodated in a metal housing attached to the exhaust pipe 22. The electrodes 3 and 4 are provided so as to be electrically insulated from the housing.

  The wirings 24 and 25 connected to the electrodes 3 and 4 are connected to the circuit unit 26. The circuit unit 26 is a combination of the temperature raising circuit 6, the detection circuit 5, and the connection point 9 of FIG. The DPF regeneration is controlled by an electronic control unit (ECU) (not shown). Therefore, the circuit unit 26 is preferably arranged around the ECU. For this reason, the wirings 24 and 25 are provided from the DPF 23 to the periphery of the ECU.

  Although not shown, a conventional retarder is provided in a vehicle to which the present invention is applied. The temperature raising circuit 6 in FIG. 1 is configured so that the regenerative current of the retarder is converted into a direct current by a direct current circuit and applied between the two electrodes 3 and 4.

  As shown in FIG. 3, the equivalent capacitor 31 represents a capacitor configured by sandwiching the filter body 2 between the electrodes 3 and 4 as shown in FIG. 1. The capacitance of the equivalent capacitor 31 changes according to the amount of PM accumulated in the filter body 2. For this reason, the response signal (amplitude and phase) when an alternating current is applied between the electrodes 3 and 4 changes according to the amount of PM. Therefore, the PM amount can be detected by detecting the change in the response signal.

  Hereinafter, the operation of the DPF system 1 according to the present invention will be described.

  The detection circuit 5 periodically applies an alternating current between the electrodes 3 and 4 during operation of the engine 21 to detect a change in the response signal. Since the change in the response signal corresponds to the amount of PM accumulated in the filter main body 2, by setting a threshold value for determining the DPF regeneration timing with respect to the change in the response signal by an experiment in advance, The DPF regeneration time can be determined from the change.

  At the DPF regeneration time, the temperature raising circuit 6 applies a direct current between the electrodes 3 and 4. The filter body 2 made of silicon carbide is a semiconductor and generates heat when a direct current flows. Thus, PM accumulated in the filter body 2 can be incinerated by raising the temperature of the filter body 2 by its own heat generation.

  As described above, according to the present invention, since the electrodes 3 and 4 are provided so as to be in contact with the outer periphery of the filter body 2 and face each other, a structure in which no heating wire or electrode is incorporated in the filter body 2 is provided. Simple structure and easy manufacture.

  According to the present invention, since a current flows through the filter body 2 itself made of silicon carbide, it is possible to raise the temperature over a wide range, unlike the case using a heating wire.

  According to the present invention, current flows uniformly in the filter body 2 from the entire surface of the electrode 3 toward the entire surface of the electrode 4, thereby forming a temperature distribution as shown in FIG. 1. That is, the central portion becomes the highest temperature high temperature portion H, and the periphery of the high temperature portion H becomes the intermediate temperature portion M having a slightly lower temperature than the high temperature portion H. Although the temperature around the intermediate temperature portion M is still lower, the temperature is still high enough to incinerate PM. Since the place where the most PM is accumulated is the central portion, the central portion becomes the high temperature portion H, so that the PM can be effectively incinerated.

  According to the present invention, the amount of PM can be detected by applying an alternating current between the electrodes 3 and 4.

  According to the present invention, since the electrodes 3 and 4 are provided on the outer periphery of the filter body 2, PM does not adhere to the electrodes 3 and 4. If the electrode is on the end face or inside of the filter main body 2, it touches the exhaust gas, so that PM adheres to the electrode and pressure loss increases, leading to an increase in exhaust pressure of the engine 21. Since the electrode is not a heating wire and there is no heater effect, PM adhering to the electrode cannot be incinerated.

  According to the present invention, since the temperature raising circuit 6 raises the temperature of the filter body 2 using the regenerative current of the retarder, the burden on the battery can be reduced. Since the retarder can generate a large amount of power, it is suitable for increasing the temperature of the filter body 2 that requires a large current.

  According to the present invention, the electrodes 3 and 4 are used both for applying an alternating current for detecting the amount of PM and for applying a direct current for raising the temperature. Is suppressed.

  According to the present invention, since the alternating current of the detection circuit 5 and the direct current of the temperature raising circuit 6 are superimposed via the AC coupling capacitor 8, the wiring from the connection point 9 to the electrodes 3 and 4 is a direct current wiring. It is more economical than providing separate wiring for AC current.

DESCRIPTION OF SYMBOLS 1 DPF system 2 Filter body 3, 4 Electrode 5 Detection circuit 6 Temperature rising circuit

Claims (2)

A porous filter body made of silicon carbide for collecting particulate matter;
Two electrodes in contact with the outer periphery of the filter body and facing each other;
A detection circuit for detecting the amount of particulate matter accumulated in the filter body based on a change in a response signal when an alternating current is applied between the two electrodes;
Diesel particulates comprising: a temperature raising circuit for incinerating particulate matter accumulated in the filter body by applying a direct current between the two electrodes to raise the temperature of the filter body Filter system.   2. The diesel particulate filter system according to claim 1, wherein the temperature raising circuit converts the regenerative current of the retarder into a direct current and applies it between the two electrodes.

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