JP5736967B2 - DPF regeneration end time determination device - Google Patents

Description

  The present invention relates to a DPF regeneration end time determination device that can accurately determine the end time of DPF regeneration.

  In a vehicle equipped with an internal combustion engine such as a diesel engine, a diesel particulate filter (hereinafter referred to as DPF) is installed in an exhaust gas exhaust flow path from the internal combustion engine to the atmosphere, and particulate matter ( Particulate Matter (hereinafter referred to as PM) is collected. The DPF is a member that temporarily collects PM in a honeycomb pore filter made of porous ceramic.

  When the amount of PM collected in the DPF (hereinafter referred to as PM accumulation amount) increases, the exhaust pressure of the internal combustion engine rises and the characteristics of the internal combustion engine deteriorate, so the process of burning the collected PM is performed. Is called. This process is called DPF regeneration. During the DPF regeneration, fuel injection for increasing the exhaust temperature is performed. When the exhaust gas temperature rises, the DPF is heated up and the PM collected in the DPF burns.

  It is known that the timing of starting DPF regeneration is determined by detecting the pressure difference between the upstream and downstream of the DPF, or by detecting the capacitance between two electrodes installed in the DPF. That is, when the amount of PM accumulated in the DPF increases, the flow of exhaust gas is blocked and the pressure difference between the upstream and downstream of the DPF increases, so it is possible to determine by setting a threshold value for the pressure difference. . Also, since PM is a mixture of dielectric and conductor, the capacitance between the two electrodes installed in the DPF is proportional to the amount of PM deposited on the entire DPF. Judgment is possible by setting a threshold value.

JP 2010-274756 A JP 2010-285958 A

  As described above, the timing for starting DPF regeneration can be determined. However, it is difficult to determine the end of DPF regeneration.

  Since the pressure difference between the upstream and downstream of the DPF is affected by the exhaust gas flow rate, it is difficult to detect accurately. In the regeneration start time, since the pressure difference is large, the influence of the exhaust gas flow rate is relatively small, and the pressure difference can be accurately detected. On the other hand, in the regeneration end time, since the pressure difference becomes smaller, the influence of the exhaust gas flow rate becomes relatively large, and it is not easy to accurately detect the pressure difference. For this reason, it is difficult to accurately determine the reproduction end time.

  If the regeneration end time is not accurately determined and the regeneration ends without being completed, unburned PM remains, so the next regeneration start time comes earlier, and the frequency of DPF regeneration Higher fuel consumption. Conversely, if the regeneration is actually completed and PM is not left, but the regeneration is continued, extra fuel will be injected, and the fuel efficiency will deteriorate.

  Even in the method of estimating and determining the PM deposition amount from the electrostatic capacity, as regeneration progresses and the PM decreases, the PM deposition amount becomes minute, so the noise component becomes relatively large and the regeneration ends. It becomes difficult to accurately determine the time.

  Therefore, an object of the present invention is to provide a DPF regeneration end time determination device that can solve the above-described problems and can accurately determine the end time of DPF regeneration.

  In order to achieve the above object, a DPF regeneration end timing determining device according to the present invention is a DPF regeneration end timing determining device that determines the regeneration end timing of a DPF inserted into an exhaust gas exhaust passage from an internal combustion engine to the atmosphere. A first electrode disposed outside the DPF, a second electrode disposed inside the regeneration limit surface, which is a limit at which the temperature becomes a regeneration temperature, in the DPF, and opposed to the first electrode; and the first electrode And a capacitance detection circuit for detecting a capacitance between the second electrode and a determination to determine that the reproduction end time is reached when the capacitance detected by the capacitance detection circuit is stably changed from a decrease. And a circuit.

  Even if the second electrode is configured by inserting a metal wire into each of a plurality of cells located along a closed curved surface imaginary inside the regeneration limit surface and shorting the plurality of metal wires to each other. Good.

  The present invention exhibits the following excellent effects.

  (1) The end time of DPF regeneration can be accurately determined.

1 is an end view of a DPF to which a DPF regeneration end time determination device showing an embodiment of the present invention is attached. It is a perspective view of DPF of FIG. It is a partial end elevation of DPF to which the present invention is applied. It is a partial sectional side view of DPF to which the present invention is applied. FIG. 2 is a partial end view of the DPF in FIG. 1. It is a characteristic view of the electrostatic capacitance change with respect to time passage in the DPF regeneration end time judging device of the present invention.

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

  As shown in FIGS. 1 and 2, the DPF regeneration end timing determination device 1 according to the present invention is the first electrode 4 disposed outside the DPF 2 and the limit at which the temperature becomes the regeneration temperature in the DPF 2. A second electrode 5 disposed inside the reproduction limit surface 3 and facing the first electrode 4; a capacitance detection circuit 6 for detecting a capacitance between the first electrode 4 and the second electrode 5; And a determination circuit 7 that determines that the reproduction end time is reached when the electrostatic capacitance detected by the detection circuit 6 changes from decreasing to stable.

  Here, the reproduction limit surface 3 will be described. When the exhaust gas temperature rises due to fuel injection during DPF regeneration, the temperature near the central axis of the DPF 2 first rises, and the surrounding temperature rises. Thereby, the combustion of PM starts from the vicinity of the central axis of the DPF 2, and the combustion gradually spreads from the inner peripheral portion toward the outer peripheral portion. However, the outer peripheral portion of the DPF 2 radiates heat to the atmosphere through a metal housing (not shown). For this reason, the temperature of the outer peripheral portion of the DPF 2 is unlikely to rise, and even if the temperature of the inner peripheral portion of the DPF 2 has reached the regeneration temperature of 800 ° C. (or 900 ° C.) or higher, the temperature of the outer peripheral portion is less than the regeneration temperature. It becomes. In the region where the temperature is lower than the regeneration temperature during DPF regeneration, the deposited PM does not burn. Therefore, in this region, the state in which PM is accumulated continues even after the DPF regeneration. This area is called a non-reproducible area. On the other hand, the region where the temperature is equal to or higher than the regeneration temperature during the regeneration of the DPF is a reproducible region, and PM deposition and combustion removal are repeated. The boundary between the reproducible area and the nonreproducible area, that is, the limit where the temperature becomes the regeneration temperature is referred to as a regeneration limit surface 3.

  If the DPF 2 reaches the regeneration temperature or more up to the outermost periphery, the allowable temperature of the housing and peripheral parts will be exceeded. Actually, the housing does not reach red heat, but it is considered that the non-renewable region formed on the outer peripheral portion of the DPF 2 serves as a heat insulating layer that protects the housing from heat.

  In the present embodiment, the DPF 2 is formed in a columnar shape, and the regeneration limit surface 3 has a cylindrical shape that is concentric with the DPF 2. The distance that the regeneration limit surface 3 is from the outermost periphery of the DPF 2 varies depending on the specifications of the DPF 2 or the specifications of the internal combustion engine and the exhaust gas discharge flow path, and may be measured by experiments.

  The 1st electrode 4 can be comprised with the cylindrical metal plate which covers the outer periphery of DPF2. Since the second electrode 5 is disposed inside the DPF 2, the honeycomb structure of the DPF 2 and the PM trapping function will be described before the details of the second electrode 5 are described.

  As shown in FIG. 3, the DPF 2 has a plurality of cells 9 that are vertically and horizontally surrounded by walls 8 made of a porous material. In the figure, the sealing is indicated by hatching. The sealed cell 9 is called a sealed cell 9a, and the unsealed cell is called an open cell 9b. As shown in the figure, both vertical and horizontal neighbors of the sealed cell 9a are open cells 9b, and both vertical and horizontal neighbors of the open cell 9b are sealed cells 9a. The end face shape of the cell 9 is a square here, but may be any shape that can be arranged continuously, such as a rectangle or a parallelogram.

  Sealing and opening are reversed between the one end face and the opposite end face. That is, in one cell 9, if one end face is sealed, the opposite end face is always open, and if one end face is open, the opposite end face is always sealed. Therefore, when the same cell 9 is viewed from one side, it becomes a sealed cell 9a, and when viewed from the opposite side, it becomes an open cell 9b.

  As shown in FIG. 4, the DPF 2 is installed in the exhaust gas discharge passage, and one of the end faces is desired upstream and the opposite end face is desired downstream. On the upstream side, exhaust gas does not flow into the sealing cell 9a, but exhaust gas flows only into the open cell 9b. Since the open cell 9b into which the exhaust gas has flowed is sealed at the opposite end face desired downstream to become a seal cell 9a, the exhaust gas passes through the wall 8 made of a porous material and is adjacent to the seal cell 9a. Move to. Since the adjacent sealing cell 9a has an open end cell 9b with the opposite end face desired downstream, the exhaust gas flows out from the open cell 9b. In this way, when exhaust gas passes through the wall 8, PM in the exhaust gas is adsorbed on the wall 8 made of the porous material. In FIG. 4, the exhaust gas flowing into one open cell 9 b is shown to move to two adjacent sealing cells 9 a, but actually the exhaust gas flowing into one open cell 9 b is adjacent vertically and horizontally. Since it moves to the four sealing cells 9a, PM is adsorbed on the four walls 8 in the vertical and horizontal directions.

  In the present embodiment, the DPF 2 has a honeycomb pore structure as shown in FIG. In order to form the second electrode 5 inside the DPF 2, a metal wire is inserted into the cell 9. Specifically, as shown in FIG. 5, metal lines (shown by black circles) 11 are respectively inserted into a plurality of open cells 9b positioned along a closed curved surface 10 that is virtually inside the reproduction limit surface 3. A plurality of metal wires 11 are short-circuited with a short-circuit wire (not shown), whereby the second electrode 5 is configured.

  As shown in FIG. 5, the second electrode 5 cannot be completely overlapped with the closed curved surface 10, but by selecting the open cell 9 b as close as possible to the closed curved surface 10 and inserting the metal wire 11, the second electrode 5 can take one round. On average, it almost overlaps the closed curved surface 10.

  The depth at which the metal wire 11 is inserted from the end face of the open cell 9b is arbitrary, but as the metal wire 11 is inserted deeper, the electrode length becomes longer, which contributes to an increase in the electrode facing area. Therefore, for example, it is preferable that the metal wire 11 reaches near the place where the opposite end face of the open cell 9b is sealed. The end face into which the metal wire 11 is inserted may be an end face that faces the upstream of the exhaust gas discharge passage or an end face that faces the downstream.

  By installing the second electrode 5 in this way, the capacitor constituted by the first electrode 4 and the second electrode 5 is formed from a concentric double cylindrical electrode plate having a predetermined inter-electrode distance and an electrode facing area. It can be regarded as a capacitor.

  As shown in FIG. 1, the capacitance detection circuit 6 detects the capacitance between the first electrode 4 and the second electrode 5.

  The determination circuit 7 processes the capacitance signal detected by the capacitance detection circuit 6 and analyzes the change in capacitance. Based on this analysis, it can be determined that the regeneration end time is reached when the electrostatic capacitance changes from decreasing to stable. The determination circuit 7 may be mounted on an electronic control unit (ECU). In this case, the output of the capacitance detection circuit 6 is sampled at an appropriate interval, a time series is accumulated, and the change is analyzed by processing the time series.

  Hereinafter, the operation of the DPF regeneration end time determination device 1 of the present invention will be described.

  As the operation of the internal combustion engine continues, PM is adsorbed on the wall 8 of each cell 9 in the DPF 2 as described with reference to FIG. Since the amount of PM deposited between the first electrode 4 and the second electrode 5 increases, the capacitance of the capacitor formed by the first electrode 4 and the second electrode 5 increases.

  Thereafter, the timing for starting DPF regeneration is determined by the conventional technique, and when DPF regeneration is started, the exhaust temperature rises due to fuel injection. In the DPF 2, the temperature around the central axis first rises, and the surrounding temperature rises. Since PM burns at a place where the regeneration temperature is higher, combustion spreads from the vicinity of the central axis to the outside.

  When the combustion exceeds the second electrode 5, PM between the first electrode 4 and the second electrode 5 is burned and decreases, so that the capacitance detected by the capacitance detection circuit 6 as shown in FIG. 6. Will decrease. When the combustion further proceeds and reaches the regeneration limit surface 3, the PM is not combusted because the region outside the regeneration limit surface 3 is a non-recoverable region. For this reason, the electrostatic capacity does not change even if more time elapses.

  When the electrostatic capacitance detected by the electrostatic capacitance detection circuit 6 changes from decreasing to stable, the determination circuit 7 determines that it is the time to end reproduction. For example, when the state in which the capacitance decrease value per unit time continues to be larger than the threshold value and then changes to a state smaller than the threshold value (bent portion of the graph in FIG. 6), or static per unit time When the state where the capacitance decrease value is smaller than the threshold value continues for a predetermined time (lower flat portion in the graph of FIG. 6), the combustion in the DPF 2 reaches the regeneration limit surface 3 and the fuel injection continues even further. Since there is no effect, it is determined that the playback end time is reached.

  As described above, according to the DPF regeneration end timing determination device 1 of the present invention, the first electrode 4 and the second electrode 5 facing each other are disposed outside and inside the regeneration limit surface 3 of the DPF 2, When the combustion during the DPF regeneration progresses and reaches the regeneration limit surface 3, the electrostatic capacity is stably changed from the decrease, so that the regeneration end time can be determined. As shown in FIG. 6, since the change in capacitance occurs significantly, the reproduction end time can be accurately determined.

  The principle that the capacitance between the first electrode 4 and the second electrode 5 is proportional to the PM deposition amount is the same as that of the conventional PM sensor used for determining the regeneration start time. The regeneration end time determination device 1 does not need such accuracy as to detect the absolute amount of the PM accumulation amount, and only needs to recognize the change in the capacitance. Therefore, the capacitance detection circuit 6 and the determination circuit 7 can be realized with a simple configuration.

  In the present embodiment of FIG. 5, the open cell 9b as close as possible to the closed curved surface 10 is selected and the metal wire 11 is inserted, so that the metal wire 11 is arranged unevenly. In order to avoid the metal lines 11 being arranged unevenly, the open cells 9b may be selected so that the metal lines 11 are arranged in a straight line for each appropriate short section.

1 DPF regeneration end time determination device 2 Diesel particulate filter (DPF)
3 Regeneration Limit Surface 4 First Electrode 5 Second Electrode 6 Capacitance Detection Circuit 7 Judgment Circuit 8 Wall 9 Cell 9a Sealing Cell 9b Open Cell 10 Closed Curve 11 Metal Wire

Claims (2)

In the DPF regeneration end time determination device for determining the regeneration end time of a diesel particulate filter (hereinafter referred to as DPF) inserted in the exhaust gas exhaust passage from the internal combustion engine to the atmosphere,
A first electrode disposed outside the DPF;
A second electrode disposed inside the regeneration limit surface, which is the limit at which the temperature becomes the regeneration temperature, in the DPF, and facing the first electrode;
A capacitance detection circuit for detecting a capacitance between the first electrode and the second electrode;
A DPF regeneration end timing determination device, comprising: a determination circuit that determines that the regeneration end timing is reached when the capacitance detected by the capacitance detection circuit changes from decreasing to stable.   The second electrode is configured by inserting a metal wire into each of a plurality of cells located along a closed curved surface imaginary inside the regeneration limit surface and short-circuiting the plurality of metal wires. The DPF regeneration end time determination device according to claim 1.