JP2009041447A - Fuel supply apparatus of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel supply apparatus of diesel engine, satisfactorily atomizing and vaporizing fuel added from an exhaust gas fuel adding valve. <P>SOLUTION: A diesel engine 10 includes: an exhaust gas fuel adding valve 88 adding a fuel to an exhaust passage upstream side of an exhaust gas aftertreatment device 55; and a fuel rail 82 for distributing the fuel from a fuel tank 120 to a fuel injection apparatus 80. The fuel supply apparatus 11 has a return passage 90a causing the fuel to flow from the fuel rail 82 toward the fuel tank 120. At least a part of return fuel that is a fuel flowing through the return passage 90a is pressurized by a fuel pressurizing pump 94, and delivered under pressure to the exhaust gas fuel adding valve 88. The return fuel that is heated up to a high temperature by receiving radiation heat of the diesel engine 10 is supplied to the exhaust gas fuel adding valve 88. The atomization and vaporization of the fuel added from the exhaust gas fuel adding valve 88 is promoted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel supply device used in a diesel internal combustion engine, and more particularly to a fuel supply device for a diesel engine provided with an exhaust fuel addition valve capable of adding fuel from an exhaust passage upstream of an exhaust aftertreatment device.

  2. Description of the Related Art Diesel-type internal combustion engines (hereinafter simply referred to as “diesel engines”) are generally provided with an exhaust aftertreatment device that treats harmful components and particulate matter in exhaust gas discharged from a cylinder. . The exhaust aftertreatment device includes an exhaust purification catalyst that purifies harmful components in the exhaust gas by a catalytic reaction, and a particulate filter mechanism (hereinafter referred to as PM) that collects particulate matter in the exhaust gas (hereinafter referred to as PM). Simply “filter mechanism”).

  Examples of the exhaust purification catalyst include a NOx occlusion reduction type catalyst that stores nitrogen oxide (NOx) in exhaust gas and reduces it to nitrogen. By supplying hydrocarbon as a reducing agent to the NOx occlusion reduction type catalyst, the occluded nitrogen oxide reacts with the hydrocarbon and is reduced to nitrogen. On the other hand, the filter mechanism includes, for example, a diesel particulate filter (DPF) that collects PM, burns the collected PM, and releases the carbon as carbon dioxide to regenerate the filter. As a method of burning the collected PM, there are a method of heating the filter with an electric heater and a method of increasing the temperature of the exhaust gas flowing through the filter. To increase the temperature of the exhaust gas, a large amount of oxygen is contained. There is a method of increasing the temperature by adding hydrocarbons as fuel to the exhaust gas.

  Thus, in a diesel engine equipped with an exhaust purification catalyst as an exhaust aftertreatment device, hydrocarbons as a reducing agent, such as so-called rich spikes, are supplied, so that fuel is contained in the exhaust gas flowing toward the exhaust purification catalyst. May be added. On the other hand, in a diesel engine having a filter mechanism as an exhaust aftertreatment device, fuel may be added to the exhaust gas flowing toward the filter mechanism in order to regenerate the filter by raising the temperature of the exhaust gas.

  In order to add fuel to the exhaust gas flowing through the exhaust aftertreatment device, in the diesel engine, in addition to the fuel injection device that supplies fuel into the cylinder, the exhaust passage is upstream of the exhaust aftertreatment device. In which a “exhaust fuel addition valve” for adding fuel is provided (see, for example, Patent Document 1).

  By the way, in recent years, bio-derived diesel fuel (hereinafter simply referred to as “biofuel”) synthesized using vegetable oils such as rapeseed oil and palm oil as raw materials may be used in diesel engines. Biofuels contain more high-boiling components than light oil, and have characteristics such as being hard to vaporize (low volatility).

  Such a biofuel may be mixed with light oil at a predetermined concentration and used in a diesel engine. For this reason, in the control technology of the diesel engine disclosed in Patent Document 1, the concentration of biofuel contained in the mixed fuel is determined based on an empty space provided downstream of the exhaust aftertreatment device (NOx storage reduction catalyst / particulate filter). The amount of fuel added at the initial stage of fuel addition is increased as compared to the case where a predetermined light oil (reference fuel) is used as the concentration of the detected biofuel increases as detected from the output of the fuel ratio sensor. The amount of fuel added is reduced. Further, as the exhaust gas temperature becomes lower, control is performed so that the difference between the fuel addition amount at the initial stage of fuel addition and the fuel addition amount at the later stage of fuel addition becomes larger than when a predetermined light oil is used.

  Thereby, even when a mixed fuel having a volatility (evaporation) different from that of the predetermined light oil (reference fuel) is used, in the vicinity of the exhaust aftertreatment device (NOx storage reduction catalyst / particulate filter). The behavior of the air-fuel ratio is brought close to the behavior when a predetermined light oil is added.

JP 2006-177313 A

  However, in the control technique described in Patent Document 1, the amount of fuel added at the initial stage of fuel addition is increased as the concentration of biofuel increases, so that when mixed fuel with a high biofuel concentration is used, exhaust gas is exhausted. The atomization and vaporization of the fuel injected from the fuel addition valve deteriorates, the injection fuel from the exhaust fuel addition valve becomes difficult to oxidize, and the generation amount of particulate matter such as soot may increase. In particular, when the exhaust aftertreatment device includes an exhaust purification catalyst that requires supply of a reducing agent, the fuel from the exhaust fuel addition valve reaches the exhaust purification catalyst without being sufficiently vaporized in the exhaust gas. Therefore, there is a possibility that a desired reducing atmosphere cannot be formed in the exhaust purification catalyst. Therefore, there is a demand for a technique that can improve the atomization and vaporization of the fuel injected from the exhaust fuel addition valve and suppress the generation of particulate matter such as soot.

  The present invention has been made in view of the above, and provides a fuel supply device for a diesel engine that can improve atomization and vaporization of fuel added from an exhaust fuel addition valve. With the goal.

  A fuel supply device for a diesel engine according to the present invention includes an exhaust fuel addition valve capable of adding fuel to an exhaust passage upstream of an exhaust aftertreatment device, and a fuel rail that distributes fuel from a fuel tank to a fuel injection device. A fuel supply device used in a diesel engine equipped with a return passage capable of flowing fuel from a fuel rail toward a fuel tank, wherein at least part of the return fuel that is fuel flowing through the return passage The pressure is increased and supplied to the exhaust fuel addition valve.

  In the fuel supply device for a diesel engine according to the present invention, a feed passage that is a fuel passage for supplying fuel to the exhaust fuel addition valve, a communication passage that connects the return passage, and a communication passage that are provided in the communication passage and taken from the return passage And a pressurized fuel pump capable of pressurizing the return fuel and pumping it to the feed passage.

  In the fuel supply apparatus for a diesel engine according to the present invention, biofuel concentration determination means for determining whether or not the biofuel concentration in the fuel is equal to or higher than a predetermined determination concentration, and the biofuel concentration is equal to or higher than the determination concentration. And control means for controlling the pressurized fuel pump to pump the return fuel to the feed passage when it is determined that there is.

  In the fuel supply device for a diesel engine according to the present invention, a first shut-off valve that is provided upstream of the pressurized fuel pump in the communication passage and can be switched between communication and shut-off of the feed passage and the return passage by an on-off valve operation; Among the feed passages, the second shut-off valve is provided on the upstream side from the junction with the communication passage, and can be switched between communication and shut-off between the feed passage and the fuel tank by an on-off valve operation. When it is determined that the biofuel concentration is equal to or higher than the determination concentration, the first cutoff valve can be opened and the second cutoff valve can be closed.

  The fuel supply device for a diesel engine according to the present invention includes a high pressure fuel pump that boosts fuel from a fuel tank and pumps the fuel to a fuel rail, and the fuel injection device receives supply of fuel boosted by the high pressure fuel pump. The exhaust fuel addition valve may be configured to inject fuel at a fuel pressure lower than that of the fuel injection device in response to the supply of fuel that has not been pressurized by the high-pressure fuel pump. it can.

  According to the present invention, in the fuel rail or the like, by supplying the return fuel that has received a radiant heat from the diesel engine to a relatively high temperature to the exhaust fuel addition valve, atomization of the fuel added from the exhaust fuel addition valve and Vaporization can be improved. Generation of particulate matter such as “soot” caused by fuel from the exhaust fuel addition valve can be suppressed.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  First, schematic configurations of the diesel engine and the fuel supply device according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a schematic configuration of a fuel supply apparatus including a diesel engine. In FIG. 1, only the main parts related to the present invention are schematically shown for the diesel engine and the fuel supply device.

  As shown in FIG. 1, a diesel engine 10 according to this embodiment is a compression self-ignition internal combustion engine that spontaneously ignites fuel by supplying fuel to an atmosphere in a combustion chamber that has been compressed to a high temperature. is there. The diesel engine 10 is mounted on an automobile (not shown) as a prime mover, and the automobile is provided with a fuel supply device 11 that supplies fuel to the diesel engine 10. Further, as a control means for controlling each component constituting the fuel supply device 11, the automobile is provided with an electronic control device 100 (hereinafter referred to as an ECU) for the diesel engine 10. In this embodiment, the ECU 100 is included in the fuel supply device 11 (system) of the diesel engine 10.

  The diesel engine 10 is a so-called direct injection type diesel engine 10 in which a fuel injection device 80 provided for each cylinder directly injects fuel into the cylinder. The diesel engine 10 includes a turbocharger 60 that compresses intake air by the kinetic energy of exhaust gas discharged from the cylinder, and a part of the exhaust gas discharged from the cylinder is taken from the exhaust passage and flows into the intake passage. A so-called exhaust gas recirculation device 70 (hereinafter referred to as an EGR device) is provided.

  The diesel engine 10 is provided with a cylinder block, a piston, a connecting rod, a crankshaft, and a cylinder head 20 (not shown) as parts of an engine body system in which a cylinder is formed. A cylinder bore is formed in the cylinder block, and a piston has a piston ring (not shown) in sliding contact with an inner wall surface (hereinafter referred to as a cylinder wall) of the cylinder bore, and reciprocates in the cylinder bore.

  A cylinder head 20 is coupled to the cylinder block so as to face the top surface of the piston and close the cylinder bore. A space surrounded by the cylinder bore, the piston, and the cylinder head 20 is a “cylinder”. In addition, the cylinder arrangement | sequence of the diesel engine 10 which concerns on a present Example is an in-line 4 cylinder.

  When the crankshaft rotates, the piston reciprocates and air is sucked into the cylinder. Further, fuel is supplied to the cylinder by a fuel injection device 80. The supplied fuel is ignited by being exposed to a high temperature atmosphere in the cylinder. The reciprocating motion of the piston caused by fuel ignition / combustion is converted into rotational motion via the connecting rod and output from the crankshaft. A crank angle sensor that detects a rotation angle position of the crankshaft (hereinafter referred to as a crank angle) is provided in the vicinity of the crankshaft, and a signal related to the detected crank angle is sent to the ECU 100.

  The cylinder head 20 is formed with an intake port 24 that guides intake air from an intake passage, which will be described later, to the cylinder on one side of the cylinder bore 20 with the axis of the cylinder bore interposed therebetween. An exhaust port 26 for discharging the exhaust gas to an exhaust passage described later is formed.

  The cylinder head 20 is provided with intake and exhaust valves (not shown) corresponding to the cylinder side openings of the intake port 24 and the exhaust port 26. These intake valve and exhaust valve are driven by receiving mechanical power from a camshaft (not shown). The intake valve and the exhaust valve are configured to be openable and closable at a predetermined timing according to the crank angle.

  When the intake valve is opened, the intake port 24 communicates with the inside of the cylinder, and the diesel engine 10 can intake air in an intake passage, which will be described later, from the intake port 24 into the cylinder. When the exhaust valve is opened, the exhaust port 26 communicates with the inside of the cylinder, and the diesel engine 10 can exhaust the exhaust gas in the cylinder from the exhaust port 26 to an exhaust passage described later. .

  Further, the diesel engine 10 includes an external air duct 41 that introduces air from outside air as an intake system component that guides air from outside air to the cylinder, and an air cleaner 42 that removes dust from the intake air (hereinafter referred to as intake air). An air flow meter (not shown) for measuring the flow rate of the intake air, an intercooler 45 for cooling the air compressed by the turbocharger 60, a throttle valve 46 for adjusting the flow rate of the intake air, and the intake air An intake manifold 48, which is a distribution pipe that distributes the gas to each cylinder, is provided. In the following description, the upstream side in the flow direction of intake air is simply referred to as “upstream side”, and the downstream side in the flow direction is simply referred to as “downstream side”.

  The downstream side of the intake manifold 48 is connected to the cylinder head 20, and the branch passage 49 communicates with the intake port 24. A surge chamber 40 a communicating with the branch passage 49 is formed on the upstream side of the branch passage 49.

  On the other hand, a throttle valve 46 is provided on the upstream side of the surge chamber 40 a in the intake manifold 48. The throttle valve 46 adjusts the flow rate of intake air taken into the cylinder (hereinafter referred to as intake air amount). The opening degree of the throttle valve 46 is controlled by the ECU 100.

  An intake pipe 47 is connected to the upstream side of the throttle valve 46. A passage 40 c formed in the intake pipe 47 communicates with the surge chamber 40 a in the intake manifold 48. An intercooler 45 is connected to the upstream side of the intake pipe 47. The intercooler 45 is configured as a heat exchanger, and cools the intake air that has been compressed by a compressor 62 of the turbocharger 60 described later and has reached a high temperature.

  An intake pipe 44 is connected to the upstream side of the intercooler 45. The passage 40e formed in the intake pipe 44 communicates with the passage 40c in the intake pipe 47 via a passage (not shown) in the intercooler 45. A compressor 62 of the turbocharger 60 is connected to the upstream side of the intake pipe 44. The passage 40 e in the intake pipe 44 communicates with the compressor 62 of the turbocharger 60.

  An intake pipe 43 is connected to the upstream side of the compressor 62 of the turbocharger 60. A passage 40 g formed in the intake pipe 43 communicates with the compressor 62 of the turbocharger 60. An air cleaner 42 is connected to the upstream side of the intake pipe 43, and an outside air duct 41 is provided on the upstream side of the air cleaner 42. The passage 40 g in the intake pipe 43 communicates with the outside air duct 41 through the air cleaner 42.

  An air flow meter (not shown) is provided on the downstream side of the element of the air cleaner 42. The air flow meter detects the amount of intake air introduced from the outside air duct 41. The air flow meter sends a signal related to the detected intake air amount to the ECU 100.

  The fresh air introduced from the outside air duct 41 passes through the air cleaner 42, the flow rate is detected by the air flow meter, and is compressed by the compressor 62 of the turbocharger 60. The compressed intake air (fresh air) that has become hot is cooled by the intercooler 45 and flows to the throttle valve 46. The intake air whose flow rate is adjusted by the throttle valve 46 flows into the surge chamber 40a of the intake manifold 48, is distributed to each cylinder from the branch passage 49, and flows into the cylinder through the intake port 24.

  The “intake passage” means a passage formed by the above-described intake system components and the intake pipe and through which the intake air introduced from the outside air duct 41 flows into the cylinder. In this embodiment, the intake passage includes not only the surge chamber 40 a in the intake manifold 48 but also the intake port 24 of the cylinder head 20.

  Further, the diesel engine 10 includes exhaust manifolds 52 that join exhaust gases from the cylinders and lead them to the turbocharger 60 as exhaust system parts that exhaust exhaust gases from the cylinders to the outside air. An exhaust aftertreatment device 55 for treating nitrogen oxides and particulate matter (PM), an oxidation catalyst 58 for purifying exhaust gas from the exhaust aftertreatment device 55 by an oxidation reaction, an oxidation catalyst 58 and an exhaust aftertreatment device 55, A / F sensor 108 is provided for detecting the oxygen concentration of the exhaust gas between the two. In the following description, the upstream side in the flow direction of the exhaust gas is simply referred to as “upstream side”, and the downstream side in the flow direction is simply referred to as “downstream side”.

  A manifold passage 50a is formed in the exhaust manifold 52, and branch portions 51 are provided on the upstream side of the manifold passage 50a corresponding to the respective cylinders. A branch portion 51 formed in the exhaust manifold 52 communicates with the exhaust port 26 of each cylinder. Further, a merging portion 50c where exhaust gases from the cylinders merge is provided on the downstream side of the manifold passage 50a. A manifold passage 50a formed in the exhaust manifold 52 joins exhaust gas discharged from a plurality of cylinders of the diesel engine 10 through the exhaust port 26 at a joining portion 50c to be a turbine 64 of a turbocharger 60 described later. Lead to.

  The turbocharger 60 includes a compressor 62 provided between the intake pipe 43 and the intake pipe 44, and a turbine 64 provided between the exhaust manifold 52 and the exhaust pipe 54. is doing. A compressor wheel (not shown) that compresses air by rotating is accommodated in the housing of the compressor 62, and a turbine wheel that is driven to rotate by the flow of exhaust gas (shown in the figure). (Not shown) is housed. The compressor wheel and the turbine wheel are joined together.

  In the turbocharger 60, the turbine wheel and the compressor wheel are rotationally driven by the kinetic energy of the exhaust gas flow flowing into the turbine 64 from the merging portion 50c of the manifold passage 50a, and the intercooler is compressed by compressing the air in the compressor 62. 45. The exhaust gas in the turbine 64 flows downstream through the passage 50e in the exhaust pipe 54 and flows into an exhaust aftertreatment device 55 described later.

  A front stage (upstream side) of the exhaust aftertreatment device 55 is provided with a NOx occlusion reduction type catalyst 55a that is an exhaust purification catalyst that occludes nitrogen oxide in exhaust gas and reduces it to nitrogen. On the other hand, a downstream side (downstream side) is provided with a DPNR catalyst system 55c that is an exhaust purification catalyst with a filter mechanism and simultaneously purifies PM and nitrogen oxides. The NOx storage reduction catalyst 55a and the DPNR catalyst system 55c are exhaust purification catalysts that require the supply of a reducing agent, and will be described in detail below.

  The NOx occlusion reduction type catalyst 55a occludes nitrogen oxides in the exhaust gas in the form of nitrate when the exhaust gas flowing through the NOx storage reduction catalyst 55a is in an oxygen-excess atmosphere (lean atmosphere) containing a large amount of oxygen. On the other hand, when the exhaust gas flowing through the NOx storage reduction catalyst 55a has a reducing atmosphere (rich atmosphere) containing a large amount of unburned hydrocarbons (hereinafter simply referred to as “HC”), The stored nitrogen oxides are reduced to nitrogen by HC as a reducing agent contained. In this way, the NOx storage reduction catalyst 55a can purify nitrogen oxides in the exhaust gas.

  On the other hand, the DPNR catalyst system 55c has a function of a diesel particulate filter (hereinafter referred to as DPF) that collects PM, burns the collected PM, and regenerates the filter by releasing it as carbon dioxide. This is a combination of the functions of the NOx storage reduction catalyst 55a described above, and it is possible to simultaneously purify PM and nitrogen oxides.

  Specifically, the DPNR catalyst system 55c collects PM in the exhaust gas flowing through the filter in a filter, and when the exhaust gas is in an oxygen-excess atmosphere, the nitrogen oxide is changed to nitrate and stored. The collected PM is oxidized by the active oxygen generated at this time and oxygen in the exhaust gas. On the other hand, when the exhaust gas flowing through the DPNR catalyst system 55c is in a reducing atmosphere (rich atmosphere), the stored nitrogen oxides are reduced to nitrogen by HC as a reducing agent contained in the exhaust gas. In both cases, PM is oxidized by the active oxygen generated at this time. In this way, the DPNR catalyst system 55c can oxidize and burn PM continuously to regenerate the filter in which PM is collected.

  An exhaust pipe 56 is connected to the downstream side of the exhaust aftertreatment device 55 described above, and a passage 50 g is formed in the exhaust pipe 56. Exhaust gas in which nitrogen oxides and PM are reduced by the exhaust aftertreatment device 55 flows through the passage 50g. An A / F sensor 108 for detecting the oxygen concentration of the exhaust gas in the passage 50g is attached to the exhaust pipe 56. The A / F sensor 108 sends a signal related to the oxygen concentration in the exhaust gas flowing into the oxidation catalyst 58 to the ECU 100 in which nitrogen oxides and PM are reduced by the passage 50g, that is, the exhaust aftertreatment device 55. .

  An oxidation catalyst 58 is provided on the downstream side of the exhaust pipe 56. The oxidation catalyst 58 oxidizes and purifies hydrocarbons and carbon monoxide contained in the exhaust gas that has passed through the exhaust aftertreatment device 55. The exhaust gas purified by the oxidation catalyst is released to the outside air.

  The “exhaust passage” means a flow path through which exhaust gas discharged from the cylinder passes before flowing into the exhaust aftertreatment device 55. In the present embodiment, the exhaust passage includes an exhaust port 26 of the cylinder head 20, a flow passage in the turbine 64, exhaust gas, in addition to the manifold passage 50 a (branch portion 51, merge portion 50 c) formed in the exhaust manifold 52. A passage 50e formed in the pipe 54 and a passage in the exhaust aftertreatment device 55 are included.

  The diesel engine 10 also has a so-called exhaust gas recirculation in which part of the exhaust gas discharged from the cylinder is taken from the exhaust passage and flows into the intake passage, and part of the exhaust gas flowing through the exhaust passage is guided to the intake passage. A device 70 (hereinafter referred to as an EGR device) is provided. The EGR device 70 includes an EGR passage that connects the exhaust passage and the intake passage, an EGR valve 77 that adjusts the flow rate of exhaust gas that flows through the EGR passage (hereinafter referred to as EGR gas), an EGR cooler 74 that cools the EGR gas, The details will be described below.

  The exhaust manifold 52 described above is provided with an EGR gas intake 71, and an EGR pipe 72 is connected to the intake 71. An EGR cooler 74 is connected to the EGR pipe 72 on the downstream side in the flow direction of the EGR gas (hereinafter simply referred to as “downstream side”). The EGR cooler 74 is constituted by a heat exchanger, and can cool the inflow EGR gas. An EGR pipe 76 is connected to the downstream side of the EGR cooler 74.

  An EGR valve 77 is disposed at the downstream end of the EGR pipe 76. The EGR valve 77 is an electromagnetically driven valve. An EGR pipe 78 is connected to the downstream side of the EGR valve 77. The EGR pipe 78 connects an EGR gas outlet 79 provided in the intake manifold 48 and an EGR valve 77. The opening degree of the EGR valve 77, that is, the flow rate of the EGR gas flowing through the EGR passage is controlled by the ECU 100.

  The “EGR passage” is formed by the EGR pipes 72, 76, 78, the EGR cooler 74, and the EGR valve 77 until the exhaust gas introduced from the intake port 71, that is, the inert gas, reaches the outlet 79. It means the flow path that passes through. In the present embodiment, the EGR passage includes not only the passage in the EGR pipes 72, 76, and 78 but also the passage formed in the EGR cooler 74 and the EGR valve 77.

  Next, the fuel supply device 11 of the diesel engine 10 according to the present embodiment will be described with reference to FIG. The fuel supply device 11 is provided for each cylinder as a device for supplying fuel into the cylinders of the diesel engine 10, and a fuel injection device 80 that directly injects fuel into the cylinders, and distributes the fuel to each fuel injection device 80. A fuel rail 82 and a high-pressure fuel pump 84 that pumps fuel to the fuel rail 82 are provided. The fuel pressurized by the high-pressure fuel pump 84 and pumped to the fuel rail 82 is distributed by the fuel rail 82 and supplied to each fuel injector 80.

  The high-pressure fuel pump 84 operates by receiving mechanical power from a camshaft (not shown) of the diesel engine 10 and sucks fuel from the fuel tank 120 to increase the pressure. The high-pressure fuel pump 84 supplies the fuel that has been pressurized to a high pressure from the fuel pipe 83 to the fuel rail 82. The operation of the high pressure fuel pump 84 is controlled by the ECU 100.

  The fuel rail 82 is configured to be capable of accumulating fuel at a predetermined fuel pressure. The fuel rail 82 distributes and supplies fuel to each fuel injector 80. High-pressure (for example, 180 MPa) fuel is supplied to the fuel rail 82 from the high-pressure fuel pump 84.

  Each fuel injection device 80 is supplied with fuel at a fuel pressure boosted by a high-pressure fuel pump 84 from a common fuel rail 82. The fuel injection device 80 is constituted by a piezo drive type fuel injection valve, and can perform so-called multistage injection, in which fuel is injected a plurality of times in one cycle. The injection period of the fuel injection device 80 in each cycle, that is, the injection timing and the injection time length (valve opening time) are controlled by the ECU 100 via a driver unit (not shown).

  Since the fuel injection device 80 injects fuel at the fuel pressure increased by the high-pressure fuel pump 84, the injected fuel from the fuel injection device 80 is atomized compared to the injected fuel from the exhaust fuel addition valve 88 described later. Has been. In addition, since the fuel injection device 80 injects fuel into a high-temperature atmosphere formed in the cylinder, most of the fuel from the fuel injection device 80 is combusted and exhaust gas discharged from the cylinder. In addition, a sufficiently vaporized fuel, that is, an unburned hydrocarbon as a reducing agent (hereinafter simply referred to as “HC”) can be included.

  The fuel supply device 11 has an exhaust fuel addition valve 88 as a device for supplying fuel to the exhaust passage, in addition to the fuel injection device 80 for supplying fuel into the cylinder. The exhaust fuel addition valve 88 is configured by an electromagnetically driven fuel injection valve, and the injection hole is exposed to the exhaust port 26 (exhaust passage).

  The exhaust fuel addition valve 88 is provided in the vicinity of the exhaust port 26 of the cylinder having the shortest exhaust path from the exhaust port 26 to the turbine 64 among a plurality of cylinders in the diesel engine 10. The exhaust fuel addition valve 88 injects fuel from the nozzle hole exposed in the exhaust port 26 toward the joining portion 50c, thereby adding fuel to the exhaust gas from the cylinder and supplying the exhaust aftertreatment device 55 to the exhaust aftertreatment device 55. It is possible to supply hydrocarbon as a reducing agent. The ECU 100 controls the fuel injection period of the exhaust fuel addition valve 88, that is, the injection timing and the injection time length (valve opening time).

  The fuel supply device 11 is a device that supplies the fuel from the fuel tank 120 to the high-pressure fuel pump 84 and the exhaust fuel addition valve 88, and uses the fuel in the fuel tank 120 as the high-pressure fuel pump 84 and the exhaust fuel addition valve 88. A low-pressure fuel pump 122 that pumps toward the fuel, a fuel pipe 81 that leads the fuel from the low-pressure fuel pump 122 to the high-pressure fuel pump 84, and a fuel pipe 85 that leads the fuel from the high-pressure fuel pump 84 to the exhaust fuel addition valve 88, 86.

  One end of fuel pipes 85 and 86 (hereinafter referred to as feed pipes) for supplying fuel to the exhaust fuel addition valve 88 is connected to the other end of the feed pipe 86. 98 is connected. One end of a feed pipe 85 is connected to the upstream side of the second shut-off valve 98 in the fuel flow direction (hereinafter simply referred to as “upstream side”), and the other end of the feed pipe 85 is connected to the high-pressure fuel pump 84. It is connected. One end of a fuel pipe 81 is connected to the upstream side of the high-pressure fuel pump 84, and the low-pressure fuel pump 122 is connected to the other end of the fuel pipe 81. A fuel filter 124 is provided in the middle of the fuel pipe 81.

  The fuel stored in the fuel tank 120 is pressurized by the low-pressure fuel pump 122, dust is removed by the fuel filter 124, and the fuel is pumped to the high-pressure fuel pump 84. Most of the fuel supplied from the fuel tank 120 to the high-pressure fuel pump 84 is boosted by the high-pressure fuel pump 84 and supplied to the fuel injection device 80 via the fuel pipe 83 and the fuel rail 82. At the same time, a part of the fuel supplied to the high-pressure fuel pump 84 is supplied to the exhaust fuel addition valve 88 via the feed pipes 85 and 86 without being pressurized by the high-pressure fuel pump 84. That is, the feed pipes 85 and 86 lead the fuel from the fuel tank 120 exclusively to the exhaust fuel addition valve 88.

  Note that the “feed passage” means a passage that leads fuel exclusively to the exhaust fuel addition valve 88 among the fuel passages from the fuel tank 120 to the exhaust fuel addition valve 88. In this embodiment, the feed passage includes a fuel flow path (not shown) in a second shut-off valve 98 described later, in addition to the fuel passages 85a and 86a formed in the feed pipes 85 and 86, respectively. Yes.

  In addition, the fuel supply device 11 supplies a part of the fuel (hereinafter referred to as return fuel) that is supplied to the fuel rail 82 but is not used for fuel injection of the fuel injection device 80 and is returned toward the fuel tank 120. As a device for supplying to the exhaust fuel addition valve 88, at least one of a fuel pipe 90 (hereinafter referred to as a return pipe) for returning return fuel from the fuel rail 82 toward the fuel tank and return fuel flowing from the return pipe 90. Are provided in the middle of a fuel pipe (hereinafter referred to as an exhaust addition fuel pipe) and an exhaust fuel addition pipe 92 that can flow into the feed passage in the feed pipe 86, and can be pressurized to increase the fuel. The pressure fuel pump 94 and the exhaust fuel addition pipe 92 are provided on the downstream side of the pressurized fuel pump 94 so that the fuel passage in the exhaust fuel addition pipe 92 can be shut off. A first shutoff valve 96 and a second shutoff valve 98 provided between the feed pipe 86 and the feed pipe 85 and capable of shutting off between the exhaust fuel addition valve 88 and the high pressure fuel pump 84. is doing.

  One end of the return pipe 90 is connected to the fuel rail 82, and the other end is opened in the fuel tank 120. A fuel passage 90 a (hereinafter referred to as a return passage) through which return fuel from the fuel rail 82 can flow toward the fuel tank 120 is formed in the return pipe 90. The return passage 90a communicates between a pressure accumulation chamber (not shown) in the fuel rail 82 and the fuel tank 120 so that the return fuel in the pressure accumulation chamber can flow to the fuel tank 120. During operation of the diesel engine 10, the fuel pressure in the return passage 90 a is approximately the same as the pressure in the fuel tank 120.

  The return pipe 90 has one end connected not only to the fuel rail 82 but also to the fuel injector 80, and the return passage 90a directs the return fuel from the fuel injector 80 into the fuel tank 120. It is good also as a structure which returns. The return pipe 90 can be constituted by a plurality of pipes such as a vehicle body fuel pipe and a fuel hose arranged under the floor of the vehicle.

  The return pipe 90 is provided with a return fuel intake 91, and an exhaust fuel addition pipe 92 is connected to the intake 91. The other end of the exhaust fuel addition pipe 92 is connected to an outlet 99 provided in the feed pipe 86. In the exhaust fuel addition pipe 92, fuel passages 92a, 92c, and 92e described later are formed from the upstream side in the flow direction of the return fuel. The exhaust fuel addition pipe 92 can take the return fuel flowing through the return passage 90a from the intake 91, guide it to the outlet 99, and flow it to the fuel passage 86a that is a feed passage.

  In the middle of the exhaust fuel addition pipe 92, there is provided a pressurized fuel pump 94 capable of increasing the pressure of the fuel flowing into the exhaust fuel addition pipe 92 and pumping the fuel into the feed passage in the feed pipe 86. The pressurized fuel pump 94 is configured by an electric pump. When the pressurized fuel pump 94 is operated, the pressurized fuel pump 94 can be pressurized and fed toward the outlet 99, that is, the feed passage. The operation / non-operation of the pressurized fuel pump 94 is controlled by the ECU 100.

  The first shutoff valve 96 is provided upstream of the pressurized fuel pump 94 in the exhaust fuel addition pipe 92, that is, between the pressurized fuel pump 94 and the intake port 91, and between the feed passage and the return passage. It is configured to be able to switch between communication and blocking. The ECU 100 controls communication and blocking between the feed passage and the return passage, that is, opening and closing of the first cutoff valve 96.

  When the first shut-off valve 96 is opened, the return passage 90a and the feed passage (fuel passage 86a) communicate with each other, and the pressurized fuel pump 94 sucks the return fuel flowing through the return passage 90a from the intake 91 and pressurizes it. Thus, it can be pumped toward the exhaust fuel addition valve 88.

  On the other hand, when the first shut-off valve 96 is closed, the flow of fuel between the return passage 90a and the feed passage 86a is shut off, and the return fuel flowing through the return passage 90a flows into the fuel passage 92c of the exhaust fuel addition pipe 92. 92e and the fuel passage 86a. The on / off valve operation of the first shutoff valve 96 is controlled by the ECU 100.

  The “communication path” is a fuel path that connects the fuel path 86a, which is a feed path, and the return path 90a, and means a fuel flow path from the intake 91 to the outlet 99. is doing. In this embodiment, the communication passage includes fuel passages (not shown) in the first shutoff valve 96 and the pressurized fuel pump 94 in addition to the fuel passages 92a, 92c, and 92e formed in the exhaust fuel addition pipe 92. )).

  The second shut-off valve 98 is provided between the feed pipe 85 and the feed pipe 86. That is, the second shut-off valve 98 is provided on the upstream side of the outlet 99 that is a junction with the communication path in the feed path. ing. The second shutoff valve 98 is configured to be able to switch communication and shutoff between the exhaust fuel addition valve 88, the high pressure fuel pump 84 and the fuel tank 120. The ECU 100 controls communication and blocking of the exhaust fuel addition valve 88 and the high-pressure fuel pump 84, that is, opening and closing of the second cutoff valve 98.

  When the second shut-off valve 98 is opened, fuel can flow between the high-pressure fuel pump 84 and the exhaust fuel addition valve 88, and the fuel from the fuel tank 120 is not boosted by the high-pressure fuel pump 84. The fuel can be supplied to the exhaust fuel addition valve 88 at a fuel pressure (for example, 0.7 MPa to 1 MPa).

  On the other hand, when the second shutoff valve 98 is closed, the flow of fuel between the exhaust fuel addition valve 88 and the high pressure fuel pump 84 is shut off, and the fuel from the fuel tank 120 is supplied to the exhaust fuel addition valve 88. Thus, the exhaust fuel addition valve 88 can receive only the return fuel flowing from the exhaust fuel addition pipe 92 (communication path) into the feed pipe 86 (feed path).

  In the fuel supply device 11 configured as described above, the low pressure fuel pump 122 boosts the fuel in the fuel tank 120 and pumps it to the high pressure fuel pump 84. The high pressure fuel pump 84 further boosts the supplied fuel and supplies the fuel to the fuel rail 82 from the fuel pipe 83. The fuel in the fuel rail 82 is used for fuel injection of the fuel injection device 80.

  Here, when the first cutoff valve 96 is closed and the second cutoff valve 98 is opened (hereinafter referred to as an initial state), the fuel from the fuel tank 120 is supplied to the exhaust fuel addition valve 88. The high-pressure fuel pump 84 and the feed pipes 85 and 86 are supplied to the exhaust fuel addition valve 88 for fuel injection. By closing the first shutoff valve 96, the fuel in the feed passage is prevented from flowing back to the return passage through the communication passage.

  Here, the fuel rail 82 and the fuel injection device 80 are mounted on the engine body of the diesel engine 10 such as the cylinder head 20, and the fuel flowing through these components is heated by receiving radiant heat from the engine body. Is done. Therefore, the fuel that flows from the fuel rail 82 through the return pipe 90 toward the fuel tank 120, that is, the return fuel that flows through the return passage 90a, has the first cutoff valve 96 and the second cutoff valve 98 controlled to the initial state. In this case, the temperature is higher than that of the fuel supplied to the exhaust fuel addition valve 88 because of the radiant heat of the engine body. The return fuel may be heated up to about 130 ° C. depending on the operation state of the diesel engine 10.

  The fuel supply device 11 includes a control for controlling the fuel injection device 80, the exhaust fuel addition valve 88, the high-pressure fuel pump 84, the pressurized fuel pump 94, the first cutoff valve 96, the second cutoff valve 98, and the like described above. It has ECU100 as a means.

  ECU 100 is a signal related to a crank angle from a crank angle sensor (not shown), a signal related to an intake air amount from an air flow meter (not shown), and a signal related to an accelerator operation amount from accelerator pedal position sensor 102. And a signal from the A / F sensor 108 relating to the oxygen concentration in the exhaust gas after passing through the exhaust aftertreatment device 55 (before flowing in the oxidation catalyst 58).

  Based on these signals, the ECU 100 calculates various control variables. The control variables include the crankshaft rotation angle position (crank angle), the crankshaft rotation speed (hereinafter referred to as engine rotation speed), and the mechanical power output from the crankshaft by the diesel engine 10 (hereinafter referred to as engine load). The intake air amount, the accelerator operation amount, the exhaust temperature in the vicinity of the exhaust aftertreatment device 55, the oxygen concentration contained in the exhaust gas after passing through the exhaust aftertreatment device 55 and before flowing into the oxidation catalyst 58, etc. There is.

  The ECU 100 determines the fuel injection period of the fuel injection device 80, the fuel pressure of the fuel supplied from the high-pressure fuel pump 84 to the fuel rail 82, and the throttle valve 46 opening based on the operating state of the diesel engine 10 ascertained from these control variables. And the opening degree of the EGR valve 77 are determined and controlled. Further, the ECU 100 controls the operation of the pressurized fuel pump 94 and the on / off operation of the first shut-off valve 96 and the second shut-off valve 98 based on the operating state of the diesel engine 10.

  In addition, the ECU 100 can control the exhaust fuel addition valve 88 to add fuel to the exhaust gas discharged from the cylinder to the exhaust passage. The ECU 100 causes the exhaust fuel addition valve 88 to add fuel at a preset injection timing and injection time length in accordance with the cumulative operation time of the diesel engine 10, the cumulative fuel injection amount of the fuel injection device 80, and the like. It is possible.

  Under the control of the ECU 100, the exhaust fuel addition valve 88 adds fuel to the exhaust passage, thereby reducing the reducing atmosphere (rich atmosphere) in the NOx occlusion reduction type catalyst 55a and the DPNR catalyst system 55c constituting the exhaust aftertreatment device 55. Can be supplied. As a result, the nitrogen oxides stored in the NOx storage reduction catalyst 55a and the DPNR catalyst system 55c can be reduced to nitrogen. In this way, the fuel addition control of the exhaust fuel addition valve 88 executed by the ECU 100 in order to reduce the nitrogen oxides stored in the exhaust aftertreatment device 55 will be referred to as “NOx reduction control” in the following description.

  Further, by adding fuel to the exhaust passage by the exhaust fuel addition valve 88, the exhaust temperature of the exhaust gas flowing through the DPNR catalyst system 55c can be raised, and the filter mechanism constituting the DPNR catalyst system 55c can be raised in temperature. . Thereby, PM (soot etc.) collected by the filter is oxidized and released as carbon dioxide, so that the PM collecting ability of the filter can be recovered, that is, the filter can be regenerated. In this way, the fuel addition control of the exhaust fuel addition valve 88 executed by the ECU 100 in order to regenerate the filter that has collected PM will be referred to as “PM collection filter regeneration control” in the following description.

  Further, the exhaust fuel addition valve 88 adds fuel to the exhaust passage, thereby raising the exhaust temperature of the exhaust gas flowing through the exhaust aftertreatment device 55 and raising the temperature of the NOx occlusion reduction type catalyst 55a and the DPNR catalyst system 55c. be able to. Thereby, in the NOx occlusion reduction type catalyst 55a and the DPNR catalyst system 55c, the temperature of the catalyst is raised even if the NOx purification ability is reduced due to “sulfur poisoning” in which the sulfur component in the fuel is occluded as a sulfuric acid compound. At the same time, by supplying a reducing atmosphere, the sulfuric acid compound on the catalyst is oxidized and released as SOx, so that the NOx purification ability of the catalyst can be recovered, that is, the catalyst can be regenerated. In this way, the fuel addition control of the exhaust fuel addition valve 88 executed by the ECU 100 in order to regenerate the sulfur poisoned catalyst is referred to as “sulfur poisoned catalyst regeneration control” in the following description.

  The ECU 100 controls the exhaust fuel addition valve 88 in the exhaust passage when any one of these NOx reduction control, PM collection filter regeneration control, and sulfur poisoning catalyst regeneration control needs to be performed. By injecting the fuel, the fuel is added to the exhaust gas discharged from the cylinder to the exhaust passage, and the fuel is contained in the exhaust gas, thereby exhausting the reducing atmosphere containing hydrocarbons as a reducing agent. It can be formed in the post-processing device 55.

  Further, in the fuel supply device 11, the ECU 100 opens the first cutoff valve 96 and closes the second cutoff valve 98, that is, controls the first cutoff valve 96 and the second cutoff valve 98 to the initial state. Further, by operating the pressurized fuel pump 94, at least a part of the return fuel flowing through the return pipe 90 (return passage 90a) is taken into the exhaust fuel addition pipe 92 (communication passage), and the exhaust fuel is supplied. The fuel can be poured into a fuel pipe 86 (feed passage) that supplies fuel to the addition valve 88. By controlling in this way, the fuel supply device 11 can supply the exhaust fuel addition valve 88 with the return fuel that is at a high temperature by the amount of radiant heat from the engine body from the return passage 90a. It has become.

  By the way, the fuel tank 120 is made using not only diesel fuel (hereinafter referred to as light oil) produced by fractionating crude oil, which is a mineral resource, but also biological organic resources (for example, vegetable oil). In addition, biological diesel fuel (hereinafter referred to as biofuel) may be mixed and supplied at a predetermined concentration. The “biofuel” is composed of fatty acid methyl ester (FAME) or the like obtained by esterifying vegetable oil such as rapeseed oil or palm oil with methanol.

  Biofuel has a feature that it contains more high-boiling components than light oil and is difficult to vaporize. In addition, since biofuel has a higher kinematic viscosity than light oil, the fuel injected from the exhaust fuel addition valve 88 is difficult to atomize. Further, unlike light oil, biofuel contains oxygen (oxygen-containing compound) in molecules constituting the fuel, and thus has a feature that the combustion of fuel is promoted by this oxygen. In addition, it is known that such a biofuel becomes easy to atomize and vaporize as the temperature of the fuel increases.

  For this reason, in the diesel engine 10 provided with the exhaust fuel addition valve 88 that can add fuel from the upstream side of the exhaust aftertreatment device 55 in the exhaust passage, fuel in which predetermined light oil and biofuel are mixed (mixed fuel) Is used, the generation amount (discharge amount) of HC and PM (soot) due to the fuel addition of the exhaust fuel addition valve 88 changes according to the biofuel concentration (hereinafter referred to as biofuel concentration). It will be. This will be described below with reference to FIG. FIG. 2 is a conceptual diagram illustrating the amount of HC and PM (soot) discharged by adding fuel to the exhaust fuel addition valve.

  In this embodiment, the fuel supplied to the fuel tank 120 and supplied to the diesel engine 10 is a mixture of two types of fuel, a predetermined light oil and a specific type of biofuel, at a certain mixing ratio. It is assumed that things are being used. This fuel includes so-called neat fuel in which the biofuel concentration in the fuel is 100% and predetermined light oil in which the biofuel concentration is zero.

  In FIG. 2, the HC and PM emissions when the biofuel concentration is zero, that is, when only predetermined light oil is used as the fuel, are indicated by a one-dot chain line B. When the biofuel concentration is from zero to the concentration D1, the HC and PM emissions due to fuel addition decrease as the biofuel concentration increases. This is because, as the concentration of biofuel increases, the added fuel becomes more difficult to atomize and vaporize and the stoichiometric air-fuel ratio decreases, but the concentration of oxygenated compounds in the fuel increases, resulting in fuel combustion (oxidation). ) Is promoted and HC and PM emissions tend to decrease.

  When the biofuel concentration is D1 or more, as the biofuel concentration increases, the combustion promoting effect due to the increase in the oxygen-containing compound concentration is reduced, and the atomization and vaporization of the fuel deteriorates and the stoichiometric air-fuel ratio decreases. The amount of HC and PM discharged tends to increase, and when the concentration reaches a predetermined concentration D2, the amount of HC and PM discharged by the fuel addition of the exhaust fuel addition valve 88 is predetermined as fuel. This is the same as the emission amount B when only the diesel oil is used.

  In the region of the concentration D2 or higher, the HC and PM emissions are higher than the emission B when the predetermined light oil is used as the fuel, and as the biofuel concentration increases from the concentration D2, HC and There is a tendency for PM emissions to increase.

  In this way, particularly when the biofuel concentration in the fuel is equal to or higher than the predetermined biofuel concentration D2, the effect of worsening the atomization and vaporization of the fuel is caused by combustion (oxidation) by the oxygen-containing compound in the fuel. As a result, the amount of HC and PM discharged due to the fuel addition of the exhaust fuel addition valve 88 is increased as compared with the case where only predetermined light oil is used as the fuel. Therefore, in the diesel engine 10 provided with the exhaust fuel addition valve 88 for adding fuel from the exhaust passage upstream of the exhaust aftertreatment device 55, a fuel (mixed fuel) in which light oil and biofuel are mixed is used. In this case, there is a demand for a technique for promoting vaporization and atomization of the fuel injected from the exhaust fuel addition valve 88.

  Therefore, the fuel supply device 11 of the diesel engine 10 according to the present embodiment is characterized in that at least a part of the fuel flowing through the return passage 90a is taken in and supplied to the exhaust fuel addition valve 88. 1 and FIG. FIG. 3 is a flowchart of fuel supply control to the exhaust fuel addition valve executed by the ECU.

  As shown in FIG. 1, a fuel tank 120 that supplies fuel to the diesel engine 10 according to the present embodiment is provided with a biofuel concentration detection device 128 that detects a biofuel concentration in the supplied fuel. The biofuel concentration detection device 128 is configured to be able to detect fuel properties such as viscosity and temperature of the fuel supplied into the fuel tank 120. The biofuel concentration detection device 128 sends a signal related to the detected fuel property to the ECU 100. The ECU 100 detects a signal related to the fuel property, and acquires the fuel viscosity, temperature, and the like as control variables. The ECU 100 can estimate the biofuel concentration in the fuel based on the acquired control variables such as viscosity and temperature.

  Note that the method for estimating the biofuel concentration is not limited to the above. For example, the biofuel concentration detection device 128 detects the viscosity or temperature of the fuel supplied into the fuel tank 120, estimates the biofuel concentration, and sends a signal related to the estimated biofuel concentration to the ECU 100 It is also good. In this case, the ECU 100 receives a signal from the biofuel concentration detection device 128 and acquires the biofuel concentration as a control variable. In the present embodiment, the biofuel concentration detection device 128 is provided in the fuel tank 120, but may be provided in the fuel rail 82, the fuel pipes 83, 85, 86, and the high-pressure fuel pump 84.

  Further, the method of estimating the biofuel concentration is not limited to the method of detecting and estimating directly from the fuel by the biofuel concentration detection device 128 as described above. For example, in the predetermined operation state of the diesel engine 10, the fuel supply system parts such as the fuel injection device 80 are operated in the same manner as when only light oil is supplied. At this time, the exhaust gas detected from the A / F sensor 108 is operated. The ECU 100 grasps the oxygen concentration in the passage, that is, the behavior (time history) of the air-fuel ratio in the exhaust passage, and estimates the biofuel concentration by comparing with the behavior of the air-fuel ratio when only light oil is supplied. You can also.

  In the fuel supply device 11 (system) configured as described above, the ECU 100 executes the following “fuel supply control” to the exhaust fuel addition valve 88. This fuel supply control is repeatedly executed by the ECU 100 as the control means of the fuel supply device 11 when the diesel engine 10 is operated.

  In the initial state before the fuel supply control is executed, the ECU 100 controls the first shutoff valve 96 to the open state and the second shutoff valve 98 to the closed state, and further pressurizes the fuel. The pump 94 is controlled in a non-operating state. Fuel from the fuel tank 120 is supplied to the exhaust fuel addition valve 88 through a high-pressure fuel pump 84 and feed pipes 85 and 86.

  First, in step S100, the ECU 100 estimates the biofuel concentration by the above-described method and acquires it as a control variable.

  In step S102, the ECU 100 determines whether or not the biofuel concentration acquired as the control variable is equal to or higher than a predetermined determination concentration. The determination concentration is set to a biofuel concentration that makes it difficult to atomize and vaporize the fuel from the exhaust fuel addition valve 88 even when the exhaust fuel addition valve 88 injects fuel into the exhaust passage. The determination concentration is obtained in advance by a conformance experiment or the like, and is stored in a ROM (not shown) of the ECU 100 as a control constant.

  If it is determined in step S102 that the biofuel concentration is lower than the determination concentration (No), even if fuel is injected from the exhaust fuel addition valve 88, it is determined that the injected fuel is sufficiently atomized and vaporized, Proceeding to step S108, the above-described fuel addition control is executed with the first cutoff valve 96, the second cutoff valve 98, and the pressurized fuel pump 94 left in their initial states.

  On the other hand, if it is determined in step S102 that the biofuel concentration is equal to or higher than the determination concentration (Yes), it is determined that the fuel injected from the exhaust fuel addition valve 88 cannot be sufficiently atomized and vaporized. The process proceeds to step S104.

  In step S104, the ECU 100 opens the first cutoff valve 96 and closes the second cutoff valve 98. In the fuel supply device 11, the flow of fuel from the fuel tank 120 to the exhaust fuel addition valve 88 via the high-pressure fuel pump 84 is blocked at the second cutoff valve 98. At the same time, the feed passage 86a communicates with the return passage 90a via a communication passage (fuel passages 92a, 92c, 92e). As a result, the fuel supply device 11 can guide the high-temperature return fuel flowing through the return passage 90 a to the feed passage 86 a that supplies fuel to the exhaust fuel addition valve 88.

  In step S106, the ECU 100 operates the pressurized fuel pump 94 to take in the high-temperature return fuel flowing through the return passage 90a from the intake port 91 into the communication passage, pressurize it, and pump it to the feed passage 86a. In this way, the fuel supply device 11 supplies the high-temperature return fuel flowing through the return passage 90a to the exhaust fuel addition valve 88.

  In step S108, the ECU 100 causes the exhaust fuel addition valve 88 to perform fuel injection (fuel addition), and executes the above-described fuel addition control. The fuel injected from the exhaust fuel addition valve 88 and added to the exhaust passage is a return fuel having a higher temperature than the fuel supplied to the exhaust fuel addition valve 88 in the initial state, so that the exhaust gas flowing through the exhaust passage Inside, it can be atomized and vaporized relatively easily. Thereby, in the exhaust aftertreatment device 55, it is possible to form a reducing atmosphere containing sufficiently vaporized fuel (hydrocarbon) as a reducing agent. After performing such fuel addition control, the process returns to step S100.

  In this way, when the biofuel concentration is equal to or higher than the determination concentration, the fuel supply device 11 of the diesel engine 10 takes in at least a part of the return fuel that is the fuel flowing through the return passage 90a and exhausts it. It can be supplied to the exhaust passage upstream of the aftertreatment device 55.

  As described above, the fuel supply device 11 of the diesel engine 10 according to this embodiment includes the exhaust fuel addition valve 88 that can add fuel to the exhaust passage upstream of the exhaust aftertreatment device 55, and the fuel tank 120. A fuel supply device 11 having a return passage 90 a that is used in a diesel engine 10 that includes a fuel rail 82 that distributes fuel to a fuel injection device 80 and that allows fuel from the fuel rail 82 to flow toward the fuel tank 120. In this case, at least a part of the return fuel that is the fuel flowing through the return passage 90a is pressurized and supplied to the exhaust fuel addition valve 88.

  The fuel added by the exhaust fuel addition valve 88 is finely atomized by supplying the return fuel, which has received a relatively high temperature due to the radiant heat from the diesel engine 10, to the exhaust fuel addition valve 88 in the fuel rail 82. And can be vaporized. This makes it possible to suppress the generation of particulate matter such as “soot” due to fuel from the exhaust fuel addition valve.

  Further, in the present embodiment, the fuel supply device 11 has a communication passage that connects the feed passage, which is a fuel passage for supplying fuel to the exhaust fuel addition valve 88, and the return passage 90a. A pressurized fuel pump 94 that is provided and capable of increasing the pressure of the fuel taken from the return passage 90a and pumping the fuel into the feed passage is provided.

  A configuration in which at least a part of the fuel flowing through the return passage is supplied to the exhaust fuel addition valve 88 is realized by providing a communication passage that connects the feed passage and the return passage, and a pressurized fuel pump in the middle of the communication passage. can do.

  In the present embodiment, the fuel supply device 11 includes biofuel concentration determination means (ECU 100) that determines whether or not the biofuel concentration in the fuel is equal to or higher than a predetermined determination concentration. When it is determined that the biofuel concentration is equal to or higher than the determination concentration, the control unit (ECU 100) controls the pressurized fuel pump to pump the return fuel.

  When the biofuel concentration is equal to or higher than the determination concentration and it becomes difficult to atomize and vaporize the fuel from the exhaust fuel addition valve, the atomization of the fuel from the exhaust fuel addition valve can be promoted and vaporized well. . Since the pressurized fuel pump is operated only when atomization and vaporization of the fuel from the exhaust fuel addition valve becomes difficult, the mechanical or electrical energy required to operate the pressurized fuel pump is reduced. be able to.

  Further, in the present embodiment, the fuel supply device 11 is provided on the upstream side of the pressurized fuel pump 94 in the communication path, and can be switched between communication and disconnection of the feed path and the return path 90a by an open / close valve operation. A valve 96 and a second shut-off valve 98 provided upstream of the junction with the communication passage among the feed passages and capable of switching between communication and shut-off between the feed passage and the fuel tank 120 by an on-off valve operation. The ECU 100 (control means) opens the first cutoff valve 96 and closes the second cutoff valve 98 when it is determined that the biofuel concentration is equal to or higher than the determination concentration.

  This prevents the fuel in the feed passage from flowing back to the return passage via the communication passage, and when the biofuel concentration in the fuel is equal to or higher than the determination concentration, the exhaust fuel addition valve is connected to the return passage. Only fuel from can be supplied.

  Further, in this embodiment, a high-pressure fuel pump 84 that boosts the fuel from the fuel tank 120 and pumps the fuel to the fuel rail 82 is provided, and the fuel injection device 80 receives the supply of fuel boosted by the high-pressure fuel pump 84. The exhaust fuel addition valve 88 is supplied with fuel that has not been pressurized by the high-pressure fuel pump 84 and injects fuel at a fuel pressure lower than that of the fuel injection device 80. It was. Since fuel is injected at a fuel pressure lower than that of the fuel injection device 80, the fuel is added to the exhaust passage by supplying high-temperature return fuel to the exhaust fuel addition valve 88 in which atomization and vaporization of the injected fuel is relatively difficult. Atomization and vaporization can be promoted.

  In the above-described embodiment, the pressurized fuel pump 94 is operated and the return fuel is supplied toward the exhaust fuel addition valve 88 only when it is determined that the biofuel concentration is equal to or higher than the determination concentration. Although controlled, the aspect of supplying the return fuel to the exhaust fuel addition valve 88 is not limited to this. For example, regardless of the biofuel concentration in the fuel, the pressurized fuel pump 94 may be always operated to supply the return fuel to the exhaust fuel addition valve 88 when the diesel engine 10 is operated.

  In the above-described embodiment, the diesel engine 10 includes the NOx occlusion reduction type catalyst 55a and the DPNR catalyst system 55c as the exhaust aftertreatment device 55, but the exhaust of the diesel engine to which the present invention can be applied. The post-processing apparatus is not limited to this. The exhaust aftertreatment device can be applied to any diesel engine that requires fuel addition to the exhaust passage, such as an exhaust purification catalyst that requires supply of a reducing agent or a filter mechanism that needs to be heated. For example, the present invention can be applied to a diesel engine equipped with either a NOx storage reduction catalyst or a DPNR catalyst system, or a diesel engine equipped with only a diesel particulate filter (DPF).

  As described above, the control device for a diesel engine according to the present invention is suitable for a diesel engine provided with an exhaust fuel addition valve capable of adding fuel from an exhaust passage upstream of the exhaust aftertreatment device.

It is a schematic diagram which shows schematic structure of the fuel supply apparatus containing the diesel engine which concerns on an Example. It is a conceptual diagram explaining the discharge | emission amount of HC and PM (soot) by the fuel addition of an exhaust fuel addition valve. It is a flowchart of the fuel supply control to the exhaust fuel addition valve which the control apparatus (ECU) of the diesel engine which concerns on an Example performs.

Explanation of symbols

10 Diesel engine 11 Fuel supply device 26 Exhaust port (exhaust passage)
46 Throttle valve 48 Intake manifold 50a Manifold passage (exhaust passage)
50c Junction (exhaust passage)
50e passage (exhaust passage)
52 Exhaust manifold 55 Exhaust aftertreatment device 55a NOx occlusion reduction type catalyst (exhaust aftertreatment device)
55c DPNR catalyst system (exhaust aftertreatment device)
60 Turbocharger 80 Fuel injector (fuel injection valve)
82 Fuel rail 84 High pressure fuel pump 85, 86 Fuel piping 85a, 86a Fuel passage (feed passage)
88 Exhaust fuel addition valve 90 Return pipe 91 Inlet 90a Return path 92 Exhaust fuel addition pipe 92a, 92c, 92e Fuel path (communication path)
94 Pressurized fuel pump 96 1st shut-off valve 98 2nd shut-off valve 99 Outlet (merging part)
100 Electronic control device for diesel engine (ECU, control means, biofuel concentration determination means)
108 A / F sensor 120 Fuel tank 122 Low pressure fuel pump

Claims (5)

Used in diesel engines with an exhaust fuel addition valve that can add fuel to the exhaust passage upstream of the exhaust aftertreatment device and a fuel rail that distributes fuel from the fuel tank to the fuel injection device. A fuel supply device having a return passage through which fuel can flow toward a fuel tank,
A fuel supply device for a diesel engine, wherein at least a part of a return fuel that is a fuel flowing through a return passage is pressurized and supplied to an exhaust fuel addition valve. The fuel supply device for a diesel engine according to claim 1,
A feed passage that is a fuel passage that supplies fuel to the exhaust fuel addition valve, and a communication passage that connects the return passage;
A pressurized fuel pump provided in the communication path, capable of boosting the return fuel taken from the return path and pumping the return fuel to the feed path;
A fuel supply device for a diesel engine characterized by comprising: The fuel supply device for a diesel engine according to claim 2,
Biofuel concentration determination means for determining whether or not the biofuel concentration in the fuel is equal to or higher than a predetermined determination concentration;
Control means for controlling the pressurized fuel pump to pump the return fuel to the feed passage when it is determined that the biofuel concentration is equal to or higher than the determination concentration;
A fuel supply device for a diesel engine characterized by comprising: The fuel supply device for a diesel engine according to claim 3,
A first shut-off valve provided on the upstream side of the pressurized fuel pump in the communication passage and capable of switching between communication and shut-off of the feed passage and the return passage by an on-off valve operation;
A second shut-off valve provided upstream of the junction with the communication passage among the feed passages, and capable of switching between communication and shut-off between the feed passage and the fuel tank by an on-off valve operation;
Have
The control means opens the first shut-off valve and closes the second shut-off valve when the biofuel concentration is determined to be equal to or higher than the determination concentration. A fuel supply apparatus for a diesel engine, characterized in that: In the fuel supply apparatus of the diesel engine of any one of Claims 1-4,
A high-pressure fuel pump that boosts the fuel from the fuel tank and pumps it to the fuel rail,
The fuel injection device receives fuel supplied by a high-pressure fuel pump and injects fuel.
The exhaust fuel addition valve receives a supply of fuel that has not been pressurized by a high-pressure fuel pump, and injects the fuel at a fuel pressure lower than that of the fuel injection device.

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