Exhaust gas purification system and method for regenerating diesel particulate filter

Abstract

A fuel identification sensor (101) includes: an insulating layer (10); a first detection electrode (21) and a second detection electrode (22) on the insulating layer (10); and a protective layer (50) covering the first detection electrode (21) and the second detection electrode (22). The fuel identification sensor (101) detects a detection value corresponding to the dielectric constant of mixed fuel (LQ). A forced regeneration execution unit (633) executes forced regeneration of a diesel particulate filter (622). An accumulation amount estimation unit (631) estimates an accumulation amount of soot in the diesel particulate filter (622) by considering the detection value of the fuel identification sensor (101). A determination unit (632) operates the forced regeneration execution unit (633) in accordance with the accumulation amount of the soot estimated by the accumulation amount estimation unit (631).

Description

Exhaust gas purification system and method for regenerating diesel particulate filters

[0001] The present invention relates to an exhaust gas purification system and a method for regenerating a diesel particulate filter (DPF), and more particularly to an exhaust gas purification system having a diesel particulate filter and a method for regenerating a diesel particulate filter included in the exhaust gas purification system.

[0002] A DPF may be disposed in the exhaust flow path of an internal combustion engine to capture and remove particulate matter (PM), including soot, in exhaust gas emitted from the engine. Soot deposited in the DPF is removed by forced regeneration at an appropriate timing, specifically, by intentionally burning the soot. If excessive soot deposits that would be burned during forced regeneration occur, the DPF may malfunction due to overheating during combustion. On the other hand, excessively frequent forced regeneration in an attempt to avoid excessive deposition leads to a deterioration in fuel efficiency. Therefore, in order to determine the appropriate timing for forced regeneration, the amount of soot deposition may be estimated based on the operating conditions of the internal combustion engine. Furthermore, according to Japanese Patent Laid-Open Publication No. 2022-72169 (Patent Document 1), fuel characteristics are also taken into consideration when estimating the amount of soot deposition. Specifically, the cetane number is taken into consideration when estimating the amount of soot deposition, since the higher the cetane number of the fuel, the greater the amount of soot emitted from the internal combustion engine. This cetane number information is obtained from a database.

[0003] A mixture of diesel and additive fuel is sometimes used as a fuel for an internal combustion engine. In recent years, biodiesel has begun to be used as an additive fuel from the viewpoint of carbon neutrality (see, for example, JP 2023-120700 A (Patent Document 2)).

[0004] Japanese Patent Laid-Open Publication No. 2009-210568 (Patent Document 3) discloses a fluid identification method for accurately identifying the fluid type, concentration, presence / absence, and temperature of a fluid to be identified stored in a tank or the like. According to this method, a characteristic measurement value is measured as an index value indicating the characteristics of the fluid to be identified. The fluid is identified by comparing the characteristic measurement value with fluid identification data indicating the relationship between a previously measured fluid and the characteristic value of the fluid. The fluid to be identified may be at least one of light oil, kerosene, and heavy oil.

[0005] According to Japanese Patent Publication No. 2012-112759 (Patent Document 4), the technology of Japanese Patent Publication No. 2009-210568 is difficult to measure accurately due to the influence of engine vibration. Furthermore, when biofuel is mixed in, the viscosity does not change significantly depending on the degree of mixing, making it difficult to apply. Therefore, the technology of Japanese Patent Publication No. 2012-112759 aims to achieve more accurate viscosity measurement than conventional methods when automatically determining the quality of lubricating oil and diesel fuel used in diesel engines. Specifically, a determination unit is installed in the diesel engine. While the diesel engine is running, the lubricating oil on-off valve and fuel on-off valve in the determination unit are controlled to sample predetermined amounts of lubricating oil and diesel fuel into the oil chamber and fuel chamber, respectively. After the diesel engine is stopped and vibration is eliminated, the viscosity of the sampled lubricating oil and diesel fuel is measured using the lubricating oil viscosity sensor and fuel viscosity sensor. Based on the measurement results, the quality of the lubricating oil and diesel fuel is determined by the control device.

[0006] JP 2022-72169 A JP 2023-120700 A JP 2009-210568 A JP 2012-112759 A

[0007] Among the various fuel characteristics, cetane value is not the only factor that affects the amount of soot deposition in a DPF. In particular, when a blend of diesel and additive fuel is used, the blend ratio significantly affects the amount of soot deposition. Specifically, even under the same driving conditions, the greater the proportion of biodiesel in the additive fuel, the more likely soot is to be generated. Therefore, it is desirable to estimate the amount of deposition by taking into account the blend ratio of the blended fuel. If the main process for this consideration relies heavily on a database, as in the technology described in JP 2022-72169 A, creating the database in advance requires a great deal of effort. On the other hand, the technology described in JP 2009-210568 A has difficulty in accurately detecting the blend ratio, and the technology described in JP 2012-112759 A, which claims to be an improvement over the technology, significantly complicates the system.

[0008] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a technology that can improve fuel efficiency and prevent DPF failure with little effort.

[0009] Aspect 1 is an exhaust gas purification system for purifying exhaust gas from an internal combustion engine (611) that burns a mixed fuel (LQ) of diesel oil and an additive fuel, and includes a diesel particulate filter (622) configured to collect soot in the exhaust gas, a fuel discrimination sensor (101), and a control unit (630). The fuel discrimination sensor (101) includes an insulating layer (10), a first detection electrode (21) provided on the insulating layer (10), a second detection electrode (22) provided on the insulating layer (10) at a distance from the first detection electrode (21), and a protective layer (50) made of an insulator that covers the first detection electrode (21) and the second detection electrode (22). The fuel discrimination sensor (101) is configured to detect a detection value corresponding to the dielectric constant of the mixed fuel (LQ) by being arranged so that the mixed fuel (LQ) faces each of the first detection electrode (21) and the second detection electrode (22) via the protective layer (50). The control unit (630) includes: a forced regeneration execution unit (633) configured to execute forced regeneration of raising the temperature of the diesel particulate filter (622) so that the soot is removed from the diesel particulate filter (622) by burning the soot, an accumulation amount estimation unit (631) configured to estimate the amount of soot deposited in the diesel particulate filter (622) in consideration of the detection value of the fuel discrimination sensor (101), and a determination unit (632) configured to operate the forced regeneration execution unit (633) in accordance with the amount of soot deposited estimated by the accumulation amount estimation unit (631).

[0010] Aspect 2 is the exhaust gas purification system according to aspect 1, wherein the protective layer (50) of the fuel identification sensor (101) is mainly composed of zirconia or alumina and has a thickness of 1 μm or more and 10 μm or less.

[0011] Aspect 3 is the exhaust gas purification system according to aspect 1 or 2, wherein the insulating layer (10) and the protective layer (50) of the fuel discrimination sensor (101) are sintered to each other.

[0012] Aspect 4 is an exhaust gas purification system according to any one of Aspects 1 to 3, wherein in the fuel identification sensor (101), the first detection electrodes (21) and the second detection electrodes (22) are alternately positioned to form a line and space pattern (PT) having a line width (WL) and a space width (WS).

[0013] Aspect 5 is the exhaust gas purification system according to aspect 4, wherein the space width (WS) of the fuel discrimination sensor (101) is 200 μm or less.

[0014] Aspect 6 is the exhaust gas purification system according to any one of Aspects 1 to 5, wherein the added fuel includes biodiesel.

[0015] Aspect 7 is a method for regenerating a diesel particulate filter (622) included in an exhaust gas purification system for collecting soot in exhaust gas from an internal combustion engine (611) that burns a mixed fuel (LQ) of diesel oil and an additive fuel, the method comprising the step of detecting a detection value corresponding to the dielectric constant of the mixed fuel (LQ) by a fuel discrimination sensor (101), the fuel discrimination sensor (101) comprising an insulating layer (10), a first detection electrode (21) provided on the insulating layer (10), a second detection electrode (22) provided on the insulating layer (10) at a distance from the first detection electrode (21), and an insulator covering the first detection electrode (21) and the second detection electrode (22). a protective layer (50), and the fuel discrimination sensor (101) is arranged so that the mixed fuel (LQ) faces each of the first detection electrode (21) and the second detection electrode (22) via the protective layer (50), and the method further includes the steps of: estimating an amount of soot deposited in the diesel particulate filter (622) in consideration of the detection value detected by the fuel discrimination sensor (101); and performing forced regeneration to remove the soot from the diesel particulate filter (622) by increasing the temperature of the diesel particulate filter (622) when the amount of deposition exceeds a predetermined threshold.

[0016] According to aspect 1 or 7, when estimating the amount of soot deposited in the diesel particulate filter, a detected value corresponding to the dielectric constant of the blended fuel is taken into consideration. Here, the dielectric constant of the blended fuel is correlated with the mixture ratio of the blended fuel. Therefore, the amount of soot deposited can be estimated taking the mixture ratio of the blended fuel into consideration, thereby improving estimation accuracy. This prevents the timing of forced regeneration of the diesel particulate filter from being too early or too late. First, by avoiding an excessively early timing, fuel economy (energy efficiency) can be improved. Second, by avoiding an excessively late timing, failure of the diesel particulate filter due to clogging or overheating during forced regeneration can be prevented. Third, information corresponding to the fuel mixture ratio is automatically obtained based on the detected value of the fuel discrimination sensor. Therefore, obtaining this information does not require significant effort. From the above, fuel economy can be improved and failure of the diesel particulate filter can be prevented with little effort.

[0017] According to the second aspect, the protective layer is made primarily of zirconia or alumina, thereby ensuring the long-term reliability of the fuel discrimination sensor. Furthermore, the protective layer has a small thickness of 10 μm or less, thereby increasing the sensitivity of the fuel discrimination sensor to distinguish differences in the dielectric constant of blended fuels. This allows the amount of soot deposited in the diesel particulate filter to be estimated more accurately. Therefore, the timing of forced regeneration of the diesel particulate filter can be further optimized.

[0018] According to aspect 3, the insulating layer and the protective layer of the fuel discrimination sensor are sintered together. By being disposed inside a sintered body made of the insulating layer and the protective layer, the first detection electrode and the second detection electrode are more adequately protected. This allows the protective layer to be made relatively thin while still ensuring sufficient reliability. This increases the sensitivity of the fuel discrimination sensor to distinguish differences in the dielectric constant of blended fuels. Therefore, the amount of soot accumulated in the diesel particulate filter can be more accurately estimated. Therefore, the timing of forced regeneration of the diesel particulate filter can be more optimized.

[0019] According to the fourth aspect, the sensitivity of the fuel discrimination sensor to discriminate between differences in the dielectric constant of the blended fuels is easily increased. This allows the amount of soot deposited in the diesel particulate filter to be estimated more accurately. This makes it possible to further optimize the timing of forced regeneration of the diesel particulate filter. Furthermore, according to the fifth aspect, the sensitivity can be further increased.

[0020] In the sixth aspect, although the difference in the dielectric constant between the diesel fuel and the added fuel is not so large, the sensitivity of the fuel discrimination sensor is increased as described above, so that the accuracy of the correspondence relationship between the detection value of the fuel discrimination sensor and the blend ratio of the mixed fuel can be made more sufficient.

[0021] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

[0022] 1 is a schematic diagram showing an example of the configuration of an internal combustion engine system equipped with an exhaust gas purification system in one embodiment. FIG. 2 is an enlarged cross-sectional view showing the configuration of a DPF in FIG. 1. FIG. 3 is a block diagram showing the configuration of a part of an ECU in FIG. 1 that is related to the exhaust gas purification system. FIG. 4 is a flow chart showing a DPF regeneration method in one embodiment. －４10 is a graph showing an example of calculation results of the absolute value of admittance detected by a fuel discrimination sensor when estimated in μS / cm. FIG. 11 is a graph showing an example of measurement of admittance for diesel fuel and a blended fuel (with a biodiesel ratio of 10%). FIG. 12 is a front view schematically showing the configuration of a measurement system having a fuel discrimination sensor in one embodiment. FIG. 13 is a schematic rear view of FIG. 7. FIG. 14 is a schematic partial cross-sectional view taken along line IX-IX in FIGS. 7 and 8. FIG. 15 is a schematic partial cross-sectional view taken along line X-X in FIGS. 7 and 8. FIG. 16 is a schematic partial cross-sectional view showing the state during implementation of an electrical characteristic measurement method in the field of view of FIG. 10. FIG. 17 is a circuit diagram showing an approximate equivalent circuit corresponding to FIG. 11. FIG. 18 is a schematic front view showing the configuration of the fuel discrimination sensor in the measurement system of FIG. 7, with the protective layer omitted. FIG. 19 is a partial cross-sectional view schematically showing a step in a method of manufacturing a fuel discrimination sensor in one embodiment.

[0023] Hereinafter, an embodiment will be described with reference to the drawings.

[0024] <Internal Combustion Engine System> Figure 1 is a schematic diagram showing an example of the configuration of an internal combustion engine system according to one embodiment. In this embodiment, engine 611 (internal combustion engine) is a diesel engine. An intake pipe 613b is connected to an intake port of engine 611 via an intake manifold 613a, and an exhaust pipe 616b is connected to an exhaust port of engine 611 via an exhaust manifold 616a. Intake manifold 613a and intake pipe 613b form an intake passage 613. Exhaust manifold 616a and exhaust pipe 616b form an exhaust passage 16. A compressor 617a of a turbocharger 617 equipped with a boost pressure control means and an intercooler 618a that cools the intake air compressed by turbocharger 617 are respectively provided in intake pipe 613b, and a turbine 617b of turbocharger 617 is provided in exhaust pipe 616b. Although not shown, the rotor of compressor 617a and the rotor of turbine 617b are connected by a shaft. The energy of exhaust gas emitted from engine 611 rotates compressor 617a via turbine 617b and the shaft, and the rotation of compressor 617a compresses the intake air in intake pipe 613b. An intake throttle valve 626a that can adjust the flow rate of intake air is provided in intake pipe 613b downstream of compressor 617a.

[0025] The purification unit CL, which is the part where exhaust gas purification is performed, has a diesel oxidation catalyst (DOC) 621, such as a platinum-based catalyst, which functions as a NOx catalyst and an oxidation catalyst, a DPF 622, and a collector 624. Specifically, the DOC 621 and the DPF 622 are provided in this order from the engine side (exhaust gas upstream side) midway through the exhaust pipe 616b. The DOC 621 and the DPF 622 are housed in a cylindrical collector 624 that has an enlarged diameter in the exhaust pipe 616b.

[0026] The platinum-based catalysts of DOC621 are platinum-alumina catalysts, platinum-zeolite catalysts, or platinum-zeolite-alumina catalysts. The platinum-alumina catalyst is constructed by coating a honeycomb carrier made of cordierite with a slurry containing gamma-alumina powder and then supporting Pt. The platinum-zeolite catalyst is constructed by coating a honeycomb carrier made of cordierite with a slurry containing hydrogen ion-exchanged zeolite powder (H-ZSM-5) and then supporting Pt. The platinum-zeolite-alumina catalyst is constructed by coating a honeycomb carrier made of cordierite with a slurry containing hydrogen ion-exchanged zeolite powder (H-ZSM-5) and gamma-alumina powder and then supporting Pt.

[0027] The DPF 622 has a honeycomb structure. Specifically, as shown in FIG. 2 , the DPF 622 includes partition walls 622a made of ceramics such as cordierite or SiC as filter elements, and has cells, each with a polygonal cross section, that serve as fluid flow paths. The partition walls 622a are porous, or in other words, have a large number of pores. Each pore is formed to have a diameter that allows gas to pass through but prevents soot from passing through (blocking its outflow) and removing it. The DPF 622 is configured by these partition walls 622a alternately and staggeredly blocking adjacent inlet-side cells 622c and outlet-side cells 622d of a large number of parallel-formed cells 622b. Furthermore, a precious metal such as Pt or Pd may be directly supported on the partition wall 622a, or a slurry containing γ-alumina powder may be coated on the partition wall 622a, and then a precious metal such as Pt or Pd may be supported on the partition wall 622a, thereby imparting the DPF 622 with the ability to oxidize soot and hydrocarbons (HC).

[0028] Exhaust gas E1 emitted from engine 611 is oxidized by DOC 621 to remove NO, CO, and HC components. The resulting high-temperature exhaust gas flows into DPF 622 from an open cell in inlet cell 622c of DPF 622, passes through multiple pores in partition wall 622a, flows into adjacent cells, and is exhausted through outlet cell 622d at the open end. Furthermore, as exhaust gas E1 passes through each pore of partition wall 622a, the soot contained in exhaust gas E1 is blocked by each pore from flowing to adjacent cells, and accumulates in each pore and on the surface of partition wall 622a. This significantly reduces the amount of soot contained in exhaust gas E2 that has passed through DPF 622.

[0029] Furthermore, an exhaust gas recirculation (EGR) control valve 626b is attached to the engine 611 to recirculate the exhaust gas back into the intake air, with the aim of reducing NOx in the exhaust gas components and improving fuel economy. Furthermore, an EGR cooler 618b is attached to cool the exhaust gas when it is recirculated into the intake air.

[0030] Additionally, exhaust pipe 616b is provided with temperature sensors 636 and 637 for detecting the temperature of exhaust gas within exhaust pipe 616b. Temperature sensor 636 is disposed between turbine 617b and collector 624, i.e., at the inlet of DOC 621. Temperature sensor 637 is disposed at the outlet of DPF 622 to measure the temperature of exhaust gas that has passed through DPF 622. The detection outputs of temperature sensors 636 and 637 are connected to control inputs of ECU (Electronic Control Unit) 630 (controller). The detection outputs of various driving condition sensors SD are also connected to the control input of ECU 630. The driving condition sensors SD include, for example, a rotation sensor 638 for detecting the rotation speed of engine 611, an accelerator position change sensor 639 for detecting changes in accelerator position and accelerator change rate, and a mileage sensor 650 for detecting the vehicle's mileage.

[0031] A fuel injector 640 of the engine 611 is electrically connected to the ECU 630. A fuel tank 642 is connected to the fuel injector 640 via a fuel supply line 641. The fuel tank 642 stores a mixed fuel LQ. A fuel identification sensor 101 is attached to the fuel tank 642 for this mixed fuel LQ. The fuel identification sensor 101 is connected to a measuring instrument 200, and these components constitute a measurement system 500. The measurement system 500 sends a signal of the measurement result to the ECU 630. The configuration of the measurement system 500 will be described in detail below.

[0032] The ECU 630 is an electronic control unit (ECU) that controls the operation of the engine 611. The ECU has electrical circuits for control. The ECU may be configured as a microcomputer including a memory MR, a CPU (not shown), an I / O interface (not shown), and the like. The CPU is configured to execute various controls according to control programs stored in the memory MR. The ECU 630 receives various signals from sensors provided in the internal combustion engine system via the I / O interface. This allows the ECU 630 to obtain information about operating conditions, such as engine speed, exhaust gas temperature, mileage, accelerator position, and accelerator pedal change rate. The control program of the ECU 630 controls the timing and amount of fuel injection from the fuel injector 640, the opening and closing of the intake throttle valve 626a, the opening and closing of the EGR control valve 626b, and the amount of air intake by the rotation of the compressor 617a, depending on these operating conditions. In this embodiment, the control program also issues a command to execute forced regeneration of the DPF 622.

[0033] <Mixed Fuel LQ> The mixed fuel LQ is a mixture of diesel and an additive fuel. In other words, the mixed fuel LQ includes diesel and an additive fuel. The additive fuel is selected to have a relative dielectric constant different from that of diesel. The additive fuel may include biodiesel. Diesel and biodiesel may be the main components of the mixed fuel. Biodiesel is a fuel obtained by processing raw animal and vegetable oils, and is typically a fatty acid methyl ester. In this technical field, a fuel containing substantially only biodiesel is called "B100," a mixed fuel in which 10 mass% biodiesel is added to diesel is called "B10," and a mixed fuel in which 5 mass% biodiesel is added to diesel is called "B5." Although B100 is the best from a carbon-neutral perspective, it is prone to clogging of the DPF. Therefore, mixed fuel LQ is often used for internal combustion engine systems with DPFs. From the viewpoint of carbon neutrality, the mixing ratio of additive fuel to diesel is preferably 5% by mass or more, more preferably 10% by mass or more. The higher the mixing ratio, the more easily soot accumulates in the DPF. Therefore, the higher the mixing ratio, the more frequently forced regeneration of the DPF needs to be performed. Therefore, a technology is required that optimizes the timing of forced regeneration of the DPF while taking the mixing ratio into consideration. The exhaust gas purification system of the present embodiment described below meets this demand.

[0034] <Exhaust Gas Purification System> The internal combustion engine system described above includes an exhaust gas purification system having a purification unit CL (FIG. 1) and a configuration for operating the same, which will be described in detail below.

[0035] The exhaust gas purification system purifies exhaust gas from an engine 611 that burns a mixed fuel LQ of diesel and additive fuel. The exhaust gas purification system includes a purification unit CL that purifies the exhaust gas, a fuel identification sensor 101, and an ECU 630. The purification unit CL includes a DPF 622 that is configured to collect soot in the exhaust gas. The fuel identification sensor 101 is configured to detect a detection value corresponding to the dielectric constant of the mixed fuel LQ. The configuration of the fuel identification sensor 101 will be described in detail below.

[0036] When the exhaust gas flowing into the purification unit CL is hot, the soot collected by the DPF 622 is burned by the hot exhaust gas and naturally removed (natural regeneration). Soot that is not removed by natural regeneration accumulates on the filter of the DPF 622. For this reason, it is necessary to intentionally remove the soot accumulated in the DPF at an appropriate time, which is called forced regeneration. In other words, forced regeneration is an operation of increasing the temperature of the DPF 622 so that the soot accumulated in the DPF 622 is removed from the DPF 622 by burning the soot.

[0037] To increase the temperature of the DPF 622, the ECU 630 controls at least one mechanism in the internal combustion engine system that affects the temperature of the DPF 622. Such mechanisms include, for example, the fuel injector 640, the intake throttle valve 626a, and the EGR control valve 626b. If an exhaust throttle valve (not shown) is provided instead of or in addition to the intake throttle valve 626a, this may also be included in the mechanism. Specific control includes, for example, controlling the injection amount of the fuel injector 640, the injection timing of the fuel injector 640, the opening of the intake throttle valve 626a, the opening of the exhaust throttle valve (not shown), the opening of the EGR control valve 626b, or two or more of these elements. Typically, fuel is injected from the fuel injector 640 at the post-injection timing, so that the fuel is introduced into the purification unit CL, thereby increasing the temperature of the DPF 622. As a modification, a heating device for increasing the temperature of the DPF 622 may be provided in the DPF 622 .

[0038] 3 is a block diagram showing a schematic configuration of the portions of the ECU 630 related to the exhaust gas purification system. The ECU 630 has an accumulation amount estimation unit 631, a determination unit 632, and a forced regeneration execution unit 633. As a modified example, a control unit having these components may be provided as an electronic control unit separate from the ECU 630. The forced regeneration execution unit 633 is configured to execute forced regeneration. The accumulation amount estimation unit is configured to estimate the amount of soot accumulated in the DPF 622 taking into account the detection value of the fuel identification sensor 101. The determination unit 632 is configured to operate the forced regeneration execution unit 633 in accordance with the amount of soot accumulated estimated by the accumulation amount estimation unit 631.

[0039] FIG. 4 is a flowchart showing an example of a method for regenerating the DPF 621 according to an embodiment.

[0040] In step S101, the electrical characteristics of the mixed fuel LQ are detected using the fuel discrimination sensor 101. Specifically, a detection value corresponding to the dielectric constant of the mixed fuel LQ is detected by the fuel discrimination sensor 101. The detection method by the fuel discrimination sensor 101 will be described in detail later.

[0041] In step S102, the amount of soot deposited in the DPF 622 is estimated in consideration of the detection value detected by the fuel discrimination sensor 101. Specifically, a provisional estimate is calculated by provisionally estimating the amount of soot deposited using a conventional general estimation method, and a correction value is calculated in consideration of the mixture ratio of the blended fuel LQ. This consideration of the mixture ratio is performed by referring to the detection value. Then, the deposition amount is calculated as a final estimate based on the provisional estimate and the correction value.

[0042] The correction value may be, for example, a correction coefficient by which the provisional estimated value is multiplied or divided, or a correction amount by which the provisional estimated value is added or subtracted. Alternatively, a correction value corresponding to the correction coefficient and a correction corresponding to the correction amount may be calculated. The method for determining the correction amount based on the detected value by the fuel discrimination sensor 101 may be based on, for example, a predetermined arithmetic expression, or a conditional expression stored in advance in the memory MR.

[0043] A variety of conventional methods for obtaining a provisional estimate are widely known and will not be described in detail here, but typically, the provisional estimate is calculated by ECU 630 based on information represented by signals sent from driving condition sensor SD, temperature sensor 636, temperature sensor 637, etc.

[0044] The method for calculating the deposition amount as the final estimated amount is not limited to the above, and may be performed by performing any arithmetic processing on a group of values ​​including one or more values ​​represented by signals sent from the driving condition sensor SD, the temperature sensor 636, the temperature sensor 637, etc., and at least one correction value based on the detected values. In this case, the influence of the mixture ratio of the mixed fuel LQ on each of the elements representing the driving condition (e.g., engine speed, accelerator opening, and mileage) can be independently considered.

[0045] In step S103, it is determined whether the deposition amount estimated as described above exceeds a predetermined threshold value. The threshold value may be stored in the memory MR of the ECU 630 before the engine 611 is operated. The threshold value may be set depending on the material, shape, volume, etc. of the DPF 622. If the determination result is NO, the process returns to step S102. If the determination result is YES, the process proceeds to step S104.

[0046] In step S104, forced regeneration of DPF 622 is performed. That is, soot is removed from DPF 622 by raising the temperature of DPF 622. After forced regeneration is completed, the process returns to step S102. The timing to end forced regeneration may be determined based on the temperature detected by temperature sensor 624, etc.

[0047] In the above method, the detection value used by ECU 630 may be updated to the latest value at any timing as needed. In other words, the process may return to step S101 at any timing to update the detection value. The timing may be, for example, when refueling is performed or when a predetermined time has elapsed since the previous detection.

[0048] <Identification of the blend ratio of mixed fuel> The relative dielectric constants of fuels are shown below.

[0049]

[0050] A typical additive fuel to gasoline is bioethanol or biomethanol, and there is a large difference in the dielectric constant between gasoline and bioethanol or biomethanol. Therefore, it is considered relatively easy to detect their blend ratio using an electrical sensor such as a capacitance sensor. On the other hand, a typical additive fuel to diesel is biodiesel, and the difference in the dielectric constant between them is significantly smaller than the above-mentioned difference. For this reason, to the inventor's knowledge, no technology has been developed to identify the blend ratio of diesel and additive fuel in a blend with sufficient accuracy using electrical characteristics related to the dielectric constant. The inventor conducted extensive research to solve this problem and arrived at the present embodiment.

[0051] FIG. 5 shows the conductivity of the fuel for diesel and biodiesel at 1×10 －４ 1 is a graph showing the calculation results of the admittance absolute value detected by the fuel identification sensor 101 having a sensing area of ​​10 mm x 15 mm when estimated in μS / cm. The relative dielectric constant of diesel is approximately 1.8, and the relative dielectric constant of biodiesel (B100) is approximately 2.8. When the admittance absolute value is used as the detection value, the blend ratio can be identified depending on the identification accuracy of the admittance difference within the range indicated by the arrow in the figure.

[0052] 6 is a graph showing an example of measurement of the absolute admittance values ​​for diesel (0% biodiesel) and a B10 blended fuel (10% biodiesel). As can be seen from the error bars in the graph, the inventors' investigations have shown that diesel and the B10 blended fuel can be distinguished with sufficient accuracy. Furthermore, this graph suggests that it is also possible to distinguish between diesel, a B5 (5% biodiesel) blended fuel, and a B10 blended fuel with sufficient accuracy to be practically useful.

[0053] <Configuration of Measurement System> FIGS. 7 and 8 are front and rear views, respectively, illustrating the configuration of a measurement system 500 including a fuel identification sensor 101 according to this embodiment. FIG. 9 is a schematic partial cross-sectional view taken along line IX-IX in FIGS. 7 and 8. FIG. 10 is a schematic partial cross-sectional view taken along line X-X in FIGS. 7 and 8. FIG. 11 is a schematic partial cross-sectional view illustrating a state in which a method for measuring electrical characteristics is being performed in the field of view of FIG. 10. FIG. 12 is a circuit diagram illustrating an approximate equivalent circuit corresponding to FIG. 11. FIG. 13 is a schematic front view illustrating the configuration of the fuel identification sensor 101, with the protective layer 50 omitted. Note that FIGS. 7 and 8 show the mixed fuel LQ, the electrical characteristics of which are measured by the fuel identification sensor 101, using imaginary lines. FIG. 11 also shows the mixed fuel LQ. An XYZ Cartesian coordinate system is illustrated in each figure to facilitate understanding of the directional relationships between the figures. In the example shown in FIG. 1, the direction Y is parallel to the vertical direction, but the orientation of the fuel discrimination sensor 101 is not limited to this.

[0054] The measurement system 500 includes a fuel identification sensor 101 and a measuring instrument 200. The fuel identification sensor 101 is a sensor for measuring the electrical characteristics of a blended fuel LQ. The fuel identification sensor 101 includes an insulating layer 10, a first detection electrode 21, a second detection electrode 22, and a protective layer 50. The fuel identification sensor 101 may further include a first pad electrode 31, a second pad electrode 32, a first via electrode 41, and a second via electrode 42. The fuel identification sensor 101 generally includes an insulating base in which electrodes, including the first detection electrode 21 and the second detection electrode 22, are embedded. The insulating base is formed by the insulating layer 10 and the protective layer 50. The fuel identification sensor 101 is provided with a first pad electrode 31 and a second pad electrode 32 for electrical connection to the embedded electrodes from outside the fuel identification sensor 101.

[0055] The insulating layer 10 is preferably made of a ceramic insulator, and more preferably made of the same material as the protective layer 50. The thickness of the insulating layer 10 is, for example, about 1 mm.

[0056] 9 to 11, the first detection electrode 21 is provided on one surface of the insulating layer 10. The second detection electrode 22 is provided on the same surface of the insulating layer 10 at a distance from the first detection electrode 21. The minimum distance between the first detection electrode 21 and the second detection electrode 22 is preferably 30 μm or more and 2000 μm or less, and more preferably 30 μm or more and 1000 μm or less.

[0057] In the fuel identification sensor 101, the first detection electrodes 21 and the second detection electrodes 22 may be alternately positioned to form a line-and-space (L / S) pattern PT, as shown in FIG. 13 . In the example shown in FIG. 13 , the line-and-space pattern PT has a length direction along the X direction and a width direction along the Z direction. The line length LL of the line-and-space pattern PT is preferably 1 mm or more and 20 mm or less. The line-and-space pattern PT is formed by alternatingly positioning at least one line L1 (e.g., multiple lines L1 as shown in FIG. 13 ) of the first detection electrode 21 and at least one line L2 (e.g., multiple lines L2 as shown in FIG. 13 ) of the second detection electrode 22. The minimum spacing between the lines L1 and L2, i.e., the space width WS of the line-and-space pattern PT, is preferably 30 μm or more and 200 μm or less. The width of each of the lines L1 and L2, that is, the line width WL of the line and space pattern PT, is preferably 30 μm or more and 2000 μm or less, and more preferably 30 μm or more and 1000 μm or less.

[0058] The first detection electrode 21 and the second detection electrode 22 are preferably made of a high-melting-point metal that is resistant to oxidation, such as platinum, tungsten, or cobalt. The thickness of the first detection electrode 21 and the second detection electrode 22 is, for example, about 5 μm.

[0059] The protective layer 50 covers the first detection electrode 21 and the second detection electrode 22. Specifically, the protective layer 50 has a surface SF and a surface opposite the surface SF that faces the first detection electrode 21 and the second detection electrode 22. The protective layer 50 has a thickness d, which preferably satisfies 1 μm≦d≦10 μm, and more preferably 1 μm≦d≦5 μm. The protective layer 50 is made of an insulator. In particular, when the protective layer 50 is primarily composed of zirconia or alumina, the corrosion resistance and chemical resistance of the fuel identification sensor 101 are enhanced. Note that the protective layer 50 being primarily composed of zirconia or alumina means that zirconia or alumina is the predominant component in the material composition of the protective layer 50. The protective layer 50 may or may not substantially contain components other than the primary component, in other words, additive components. In the latter case, the protective layer 50 is essentially composed of zirconia or alumina. From the viewpoint of, for example, manufacturing efficiency, the protective layer 50 is preferably made of a sintered body, and the insulating layer 10 and the protective layer 50 are preferably sintered together.

[0060] Note that the protective layer 50 shown in FIGS. 7 and 9 to 11 is a single layer that continuously covers both the first detection electrode 21 and the second detection electrode 22 and does not have a particular pattern. In this case, the shape of the protective layer 50 can be simple. On the other hand, if a more complex shape of the protective layer is allowed, as a modified example, the protective layer may have some kind of pattern. This pattern may have first and second portions that are separated from each other, with the first portion covering the first detection electrode 21 and the second portion covering the second detection electrode 22. In this case, the first and second portions of the protective layer 50 are separated by an area where the protective layer 50 is not provided.

[0061] The first pad electrode 31 is provided on the surface of the insulating layer 10 opposite to the one surface. The second pad electrode 32 is provided on the surface of the insulating layer 10 opposite to the one surface, spaced apart from the first pad electrode 31. The first via electrode 41 penetrates the insulating layer 10, and has one end connected to the first detection electrode 21 and the other end connected to the first pad electrode 31. The second via electrode 42 penetrates the insulating layer 10, and has one end connected to the second detection electrode 22 and the other end connected to the second pad electrode 32.

[0062] The measuring instrument 200 is configured to detect a detection value corresponding to the dielectric constant of the blended fuel LQ to be measured. This detection value may be a complex impedance, in which case the reactance component of the complex impedance has a value corresponding to the dielectric constant of the blended fuel LQ. Alternatively, instead of the complex impedance, an extracted value from the complex impedance may be used as the detection value sent to the ECU 630. In this case, the measuring instrument 200 may have the function of measuring the complex impedance and the function of extracting the extracted value from the complex impedance according to a predetermined extraction rule. Because of the need to correlate with the capacitive reactance formed by the blended fuel LQ, the extracted value may be the reactance component of the complex impedance. However, in actual measurements, the admittance absolute value or the impedance absolute value may be more convenient. If the influence of the blend ratio on the resistance component is not significant, the admittance absolute value or the impedance absolute value may be used as the extracted value instead of the reactance component. According to the inventor's investigations, as described above with reference to FIG. 5 , the admittance absolute value can be used at least when the added fuel is biodiesel.

[0063] The measuring instrument 200 may be a typical impedance analyzer capable of measuring complex impedance, but may also be a measuring instrument that performs measurements in which information unnecessary for obtaining the above-mentioned extracted value is ignored, and the measuring instrument may have a simpler configuration than an impedance analyzer. For example, if the extracted value is the admittance absolute value, the measuring instrument does not need to measure the phase of the admittance.

[0064] The measuring instrument 200 is electrically connected to the first pad electrode 31 and the second pad electrode 32. Referring to the equivalent circuit of FIG. 12 , the complex impedance IMP is the complex impedance between the first detection electrode 21 and the second detection electrode 22 in the state shown in FIG. 11 . When detecting a detection value, as shown in FIG. 11 , the fuel identification sensor 101 is positioned so that the mixed fuel LQ faces each of the first detection electrode 21 and the second detection electrode 22 via the protective layer 50. This allows the detection value to correspond to the dielectric constant of the mixed fuel LQ. At this time, the mixed fuel LQ may be in contact with the protective layer 50. The complex impedances of the first pad electrode 31, the first detection electrode 21, and the first via electrode 41 therebetween, and the complex impedances of the second pad electrode 32, the second detection electrode 22, and the second via electrode 42 therebetween, have almost negligible effects on the complex impedance IMP. Thus, the complex impedance that meter 200 will measure is essentially the complex impedance IMP between first sensing electrode 21 and second sensing electrode 22 (FIG. 12).

[0065] The complex impedance has a resistance component and a reactance component. In the configuration of this embodiment, the reactance component is mainly due to the capacitance value formed by the protective layer 50 and the mixed fuel LQ being disposed in the electrical path between the first detection electrode 21 and the second detection electrode 22. This reactance component can be approximately regarded as the total capacitance obtained by connecting the capacitance formed through the protective layer 50 and the capacitance formed through the mixed fuel in series. Here, the larger the capacitance formed through the protective layer 50, the more likely a change in the capacitance formed through the mixed fuel is to be reflected in the total capacitance. Considering the function of the protective layer 50 to protect the first detection electrode 21 and the second detection electrode 22, zirconia or alumina is preferred as the material for the protective layer 50. In this case, the thickness d is preferably 1 μm or more and 10 μm or less.

[0066] <Method of Manufacturing Fuel Identification Sensor> FIG. 14 is a partial cross-sectional view schematically showing one step in the method of manufacturing the fuel identification sensor 101 according to this embodiment.

[0067] 9 and 14 , a laminate is prepared that includes a green sheet 10G that will become the insulating layer 10, a paste layer 21G that will become the first detection electrode 21, a paste layer 22G that will become the second detection electrode 22, a paste layer 31G that will become the first pad electrode 31, a paste layer 32G that will become the second pad electrode 32, a paste layer 41G that will become the first via electrode 41, and a paste layer 42G that will become the second via electrode 42. Each paste layer can be formed by printing a paste containing metal powder and ceramic powder onto the green sheet 10G. The green sheet 10G may be a single layer, or may be formed by stacking multiple green sheets.

[0068] A green sheet 50G that will become the protective layer 50 is pressed onto the laminate as shown by the arrow (FIG. 14). This pressing is preferably performed while heating.

[0069] Next, the laminate with the green sheet 50G pressed thereon is fired, thereby obtaining the fuel identification sensor 101. In this case, the protective layer 50 is made of a sintered body.

[0070] <Effects> According to this embodiment, when estimating the amount of soot deposited in the DPF 621, a detected value corresponding to the dielectric constant of the blended fuel LQ is taken into consideration. Here, the dielectric constant of the blended fuel LQ is correlated with the mixture ratio of the blended fuel LQ. Therefore, the amount of soot deposited can be estimated taking the mixture ratio of the blended fuel LQ into consideration, thereby improving the estimation accuracy. This prevents the forced regeneration of the DPF 621 from being too early or too late. First, by avoiding an excessively early timing, fuel economy (energy efficiency) can be improved. Second, by avoiding an excessively late timing, failure of the DPF 621 due to clogging can be prevented. Third, information corresponding to the fuel mixture ratio is automatically obtained based on the detected value of the fuel identification sensor 101. Therefore, obtaining this information does not require significant effort. As described above, fuel economy can be improved and failure of the DPF 621 can be prevented with little effort.

[0071] The protective layer 50 having zirconia or alumina as its main component ensures the long-term reliability of the fuel discrimination sensor 101. Furthermore, the protective layer 50 has a small thickness of 10 μm or less, which increases the sensitivity of the fuel discrimination sensor 101 to discriminate between differences in the dielectric constant of the blended fuel LQ. This allows the amount of soot deposited in the DPF 621 to be estimated more accurately. This allows the timing of forced regeneration of the DPF 621 to be further optimized.

[0072] As the material for the protective layer 50, zirconia is particularly preferable when priority is given to increasing the sensitivity of the fuel identification sensor 101. Alumina is particularly preferable when priority is given to suppressing the temperature dependency of the fuel identification sensor 101. Alumina is particularly preferable when priority is given to increasing the heat resistance of the fuel identification sensor 101.

[0073] The fuel identification sensor 101 having the line and space pattern PT can easily increase the sensitivity for identifying differences in the dielectric constant of the blended fuel LQ. This allows the amount of soot accumulated in the DPF 621 to be estimated more accurately. This allows the timing of forced regeneration of the DPF 621 to be further optimized. The space width WS of the line and space pattern PT is 200 μm or less, which can further increase the sensitivity. Furthermore, the space width WS is 30 μm or more, which can easily be controlled using general multilayer ceramic technology, etc.

[0074] The line length LL (FIG. 13) of the line and space pattern PT is preferably 1 mm or more and 20 mm or less. When the line length LL is 1 mm or more, the sensitivity of the fuel identification sensor 101 can be increased. When the line length LL is 20 mm or less, the probability of a defect due to the adhesion of foreign matter on the line and space pattern PT can be reduced. Furthermore, when the line length LL is 20 mm or less, the size of the fuel identification sensor 101 can be prevented from becoming excessively large.

[0075] The insulating layer 10 and the protective layer 50 of the fuel discrimination sensor 101 are sintered together. By being disposed inside a sintered body consisting of the insulating layer 10 and the protective layer 50, the first detection electrode 21 and the second detection electrode 22 are more adequately protected. This allows the protective layer 50 to be made relatively thin while still ensuring sufficient reliability. This increases the sensitivity of the fuel discrimination sensor 101 to distinguish differences in the dielectric constant of the blended fuel LQ. This allows the amount of soot accumulated in the DPF 621 to be more accurately estimated. This allows the timing of forced regeneration of the DPF 621 to be more optimized.

[0076] It is more preferable that the insulating layer 10 and the protective layer 50 are made of the same material. This reduces the difference in shrinkage rate during the firing process for manufacturing the fuel identification sensor 101. Therefore, even if the thickness d of the protective layer 50 is relatively small, a pinhole-free protective layer 50 can be obtained. Therefore, the thickness d can be further reduced while still obtaining the sufficient effect of improving the corrosion resistance and chemical resistance of the protective layer 50.

[0077] The portion that becomes the protective layer 50 is preferably formed by pressing a green sheet 50G (FIG. 14) together, which makes it possible to obtain a pinhole-free protective layer 50 even if the thickness d of the protective layer 50 is relatively small, compared to when the portion is formed by applying a ceramic paste.

[0078] The first detection electrode 21 and the second detection electrode 22 are preferably made of a high-melting point metal, such as platinum, tungsten, or cobalt, which can prevent the electrodes from volatilizing or melting during the firing process for manufacturing the fuel identification sensor 101.

[0079] 10: Insulating layer 21: First detection electrode 22: Second detection electrode 50: Protective layer 101: Fuel discrimination sensor 200: Measuring instrument 500: Measurement system 611: Engine 621: DOC (Diesel oxidation catalyst) 622: DPF (Diesel particulate filter) 624: Collector 630: ECU (control unit) 631: Deposition amount estimation unit 632: Determination unit 633: Forced regeneration execution unit 642: Fuel tank CL: Purification unit LQ: Mixed fuel PT: Line and space pattern WS: Space width

Claims

1. An exhaust gas purification system for purifying exhaust gas from an internal combustion engine (611) that burns a mixed fuel (LQ) of diesel and additive fuel, comprising: a diesel particulate filter (622) configured to collect soot in the exhaust gas; an insulating layer (10), a first detection electrode (21) provided on the insulating layer (10), a second detection electrode (22) provided on the insulating layer (10) at a distance from the first detection electrode (21), and a protective layer (50) made of an insulator that covers the first detection electrode (21) and the second detection electrode (22), and configured to detect a detection value corresponding to the dielectric constant of the mixed fuel (LQ) by being arranged so that the mixed fuel (LQ) faces each of the first detection electrode (21) and the second detection electrode (22) via the protective layer (50); and a control unit (630), wherein the control unit (630) an accumulation amount estimation unit (631) configured to estimate an accumulation amount of the soot in the diesel particulate filter (622) in consideration of the detection value of the fuel discrimination sensor (101); and a determination unit (632) configured to operate the forced regeneration execution unit (633) in accordance with the accumulation amount of the soot estimated by the accumulation amount estimation unit (631).

2. The exhaust gas purification system according to claim 1, wherein the protective layer (50) of the fuel identification sensor (101) is mainly composed of zirconia or alumina and has a thickness of 1 μm or more and 10 μm or less.

3. The exhaust gas purification system according to claim 1 or 2, wherein the insulating layer (10) and the protective layer (50) of the fuel discrimination sensor (101) are sintered together.

4. An exhaust gas purification system as described in claim 1 or 2, wherein in the fuel discrimination sensor (101), the first detection electrodes (21) and the second detection electrodes (22) are alternately positioned to form a line and space pattern (PT) having a line width (WL) and a space width (WS).

5. The exhaust gas purification system according to claim 4, wherein the space width (WS) of the fuel discrimination sensor (101) is 200 μm or less.

6. The exhaust gas purification system according to claim 1 or 2, wherein the added fuel includes biodiesel.

7. A method for regenerating a diesel particulate filter (622) included in an exhaust gas purification system for collecting soot in exhaust gas from an internal combustion engine (611) that burns a mixed fuel (LQ) of diesel oil and additive fuel, comprising the step of detecting a detection value corresponding to the dielectric constant of the mixed fuel (LQ) by a fuel discrimination sensor (101), the fuel discrimination sensor (101) including an insulating layer (10), a first detection electrode (21) provided on the insulating layer (10), a second detection electrode (22) provided on the insulating layer (10) at a distance from the first detection electrode (21), and a protective layer (50) made of an insulator that covers the first detection electrode (21) and the second detection electrode (22), the fuel discrimination sensor (101) is arranged so that the mixed fuel (LQ) faces each of the first detection electrode (21) and the second detection electrode (22) via the protective layer (50), and further A method for regenerating a diesel particulate filter (622), comprising: a step of estimating an amount of soot deposited on the diesel particulate filter (622) in consideration of the detection value detected by the fuel discrimination sensor (101); and a step of performing forced regeneration to remove the soot from the diesel particulate filter (622) by increasing the temperature of the diesel particulate filter (622) when the amount of soot deposited exceeds a predetermined threshold.

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