JP6520690B2 - Exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification system for purifying exhaust gas present in an exhaust pipe.

  In an internal combustion engine such as a diesel engine for vehicles, NOx (nitrogen oxide) is discharged by performing lean combustion. Therefore, as a technology for purifying NOx in exhaust gas, a catalyst of NOx storage reduction type in an exhaust system In many cases (hereinafter referred to as NOx catalyst). The NOx catalyst has the property of storing NOx in the exhaust gas when the atmosphere of the exhaust gas is lean in air-fuel ratio, and reducing and removing the stored NOx by reducing components such as HC and CO in the exhaust gas when the air-fuel ratio becomes rich. . However, even if the air-fuel ratio is rich, if the amount of HC and CO contained in the exhaust is small, the NOx catalyst can not reduce and remove the stored NOx.

  In the technology described in Patent Document 1, an HC supply device (hereinafter referred to as an addition valve) is attached upstream of the NOx catalyst in the exhaust pipe to supply fuel (HC) so as to be uniformly mixed in the exhaust gas. It becomes possible to reduce the stored NOx.

JP-A-8-284647

  The addition valve disclosed in Patent Document 1 is supplied with fuel from a feed pump (hereinafter referred to as a mechanical feed pump) driven directly by the engine, and is supplied with a feed pressure corresponding to the number of revolutions of the engine The fuel pressurized at pressure) is injected into the exhaust pipe.

  Although such an addition valve has a feed pressure necessary to inject fuel, the feed speed required to inject fuel properly due to the low pump rotational speed of the mechanical feed pump (mechanical feed pump) It may not reach to pressure. In this case, the addition valve can not appropriately supply the fuel to the NOx catalyst, and there is a possibility that the stored NOx can not be satisfactorily reduced and removed.

  The present invention has been made to solve the above-mentioned problems, and its main object is to stabilize the addition valve and to purify the exhaust gas in the exhaust pipe even if the rotational speed of the mechanical supply pump is in a low rotational speed region. It is an object of the present invention to provide an exhaust purification system capable of adding the following additives.

  The present invention is an exhaust gas purification system, which is disposed in an exhaust pipe of an internal combustion engine and is disposed upstream of a purification unit for purifying the exhaust gas and the purification unit in the exhaust pipe, for exhaust gas purification in the exhaust pipe. An additive valve for adding an additive, and a mechanical feed pump driven at a rotational speed according to a rotational speed of the internal combustion engine by a driving force of the internal combustion engine to pressurize the additive and supply the additive valve to the additive valve; A motor-driven feed pump driven by a motor to pressurize the additive from the additive supply source to supply the additive to the mechanical feed pump; and an additive supplied from the mechanical feed pump to the additive valve A pressure immediately before the addition valve is detected as a pressure immediately before the addition valve, and the pressure immediately before the addition valve detected by the pressure immediately before the addition valve is lower than a predetermined pressure, the pressure immediately before the addition valve is higher than the predetermined pressure Become Sea urchin, characterized in that it comprises a driving unit for driving the electric supply pump.

  An additive for exhaust gas purification is added into the exhaust pipe by the addition valve, and the exhaust gas is purified by the purification unit using the added additive. The addition valve can not properly add the additive into the exhaust pipe unless the pressure of the supplied additive reaches a predetermined pressure. Therefore, if only the mechanical supply pump is driven directly by the internal combustion engine, the pressure of the additive supplied to the addition valve is a predetermined pressure when the rotational speed of the mechanical supply pump is in the low rotation range. The mechanical feed pump may not be able to supply enough additives to reach

  In the exhaust gas purification system, an electric supply pump is provided as a countermeasure. When the immediately before the addition valve detected by the immediately preceding pressure detection unit is lower than the predetermined pressure, the drive unit drives the electric supply pump so that the immediately before the addition valve pressure becomes higher than the predetermined pressure. As a result, even if the rotational speed of the mechanical supply pump is in the low rotation range, the pressure immediately before the addition valve can be raised to a predetermined pressure by performing the supply of the additive by the electric supply pump. Thus, it becomes possible to stably add the additive into the exhaust pipe.

It is a schematic block diagram of an engine system concerning this embodiment. It is a schematic block diagram of the fuel pump of FIG. It is a figure which shows the fuel pressure of a mechanical feed pump which fluctuates depending on pump rotational speed of a mechanical feed pump. It is a control flowchart implemented by ECU concerning this embodiment. It is a figure which shows the fuel supply amount of a mechanical feed pump which fluctuates depending on pump rotational speed of a mechanical feed pump. It is a subroutine process of step S170 described in FIG. It is a control flowchart implemented by ECU which concerns on another example. It is a control flowchart implemented by ECU which concerns on another example. It is a control flowchart implemented by ECU which concerns on another example.

  Hereinafter, an embodiment in which an exhaust gas purification system according to the present invention is applied to an exhaust gas purification system of a diesel engine for a vehicle will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of an exhaust gas purification system and an engine according to the present embodiment.

  As illustrated, the fuel in the fuel tank (corresponding to a supply source) 20 is pumped up by an engine-driven fuel pump 24 driven in accordance with the rotation of the crankshaft 23. The fuel is pumped up by a fuel pump 24 via an electric feed pump (corresponding to an electric supply pump) 21 described later and a fuel filter 22.

  In the vicinity of the crankshaft 23, a crank angle sensor 27 for detecting the rotation angle of the crankshaft 23 is provided. Further, in the fuel supply path from the fuel tank 20 to the fuel pump 24, a differential pressure sensor 32 for detecting a differential pressure ΔPf of the fuel before and after passing through the fuel filter 22 is provided.

  The fuel discharged from the fuel pump 24 is pressurized and supplied (pumped) to the common rail 25 (corresponding to an accumulator). The fuel in the common rail 25 is held at a high pressure by the pumping of the fuel from the fuel pump 24, and the high pressure fuel in the common rail 25 is supplied to the injectors 11. Then, with the valve opening operation of the injector 11, the fuel is injected and supplied to each cylinder of the engine 10. Further, an intake pipe 12 and an exhaust pipe 13 are connected to the engine 10, air is introduced into the cylinder through the intake pipe 12, and exhaust gas after fuel combustion is discharged through the exhaust pipe 13.

  The exhaust pipe 13 is provided with a NOx storage / reduction type catalyst 14 (hereinafter referred to as a NOx catalyst) for purifying NOx in the exhaust as a post-treatment system for purifying exhaust gas. As well known, the NOx catalyst 14 occludes NOx contained in the exhaust at the time of lean combustion, and reduces and eliminates the occluded NOx using a reducing component such as HC or CO contained in the exhaust at the time of rich combustion. It is a thing. The NOx catalyst 14 corresponds to the purification unit.

  On the upstream side of the NOx catalyst 14 in the exhaust pipe 13, an addition valve 15 for adding and supplying a fuel (corresponding to a reducing agent) to the upstream portion of the NOx catalyst 14 is provided. A part of the low pressure fuel pumped up from the fuel tank 20 by the fuel pump 24 is supplied to the addition valve 15, and the fuel is added and supplied from the addition valve 15 into the exhaust pipe 13 with the valve opening operation. The fuel supply path from the fuel pump 24 to the addition valve 15 corresponds to a first pressure sensor (immediate pressure detection unit) that detects the pressure of fuel supplied to the addition valve 15 (hereinafter referred to as addition valve immediately before pressure P2). ) Is provided.

  In the fuel tank 20, in addition to the electric feed pump 21, a first return flow path (corresponding to a return flow path) 29 is connected. The first return flow path 29 is a flow path for returning leaked fuel from a storage chamber 54 described later that constitutes the fuel pump 24.

  The electric feed pump 21 is an electric feed pump that uses a DC motor 21 a as a power source. An electric pump driver 28 is connected to the electric feed pump 21, and an ECU 30 is connected to the electric pump driver 28. The electric pump driver 28 drives the DC motor 21a under the control of the ECU 30, and assists the fuel pump 24 to supply the fuel as needed.

  The ECU (corresponding to a drive unit) 30 is an electronic control unit mainly composed of a known microcomputer provided with a CPU, a memory and the like. Detection values of the first pressure sensor 26, the crank angle sensor 27, the differential pressure sensor 32, and a temperature sensor 55 described later are input to the ECU 30, and the memory stores detection values of various sensors. Various other programs are stored in the memory, and the CPU executes the program stored in the memory to execute the engine including the fuel injection control of the addition valve 15 and the drive control of the electric feed pump 21 and the fuel pump 24. Each part of the engine system mainly composed of 10 is controlled.

  The structure of the fuel pump 24 is shown in FIG.

  Basically, the fuel pump 24 pressurizes the fuel pumped from the fuel tank 20 by a mechanical feed pump (corresponding to a mechanical supply pump) 40 by a plunger pump (corresponding to a high pressure pump) and discharges the fuel. And the amount of fuel drawn into the plunger pump 50 is regulated by the metering valve 60.

  The mechanical feed pump 40 is a trochoid pump driven by the rotation of the crankshaft 23, and feeds the fuel, which has passed through the goose filter 41 provided to remove foreign matter contained in the fuel, to the addition valve 15 and the plunger pump 50. It functions as a low pressure supply pump. Further, the mechanical feed pump 40 not only sends the fuel to the addition valve 15 and the plunger pump 50, but also sends the fuel as the lubricating oil to the storage chamber 54 that stores the crankshaft 23. The fuel sent to the storage chamber 54 passes through an orifice 56 for throttling the passing fuel. Then, the fuel leaked from the storage chamber 54 returns to the fuel tank 20 via the first return flow passage 29. The storage chamber 54 is provided with a temperature sensor (corresponding to a temperature detection unit) 55 for detecting the temperature Thf of the fuel flowing into the storage chamber 54, and the temperature sensor 55 transmits the detected value to the ECU 30. .

  A part of the fuel supplied to the storage chamber 54 by the mechanical feed pump 40 is returned to the path between the mechanical feed pump 40 and the goose filter 41 via the second return flow path 33. A regulator valve 42 is provided in the second return flow passage 33. The regulator valve 42 causes the discharge side and the supply side of the mechanical feed pump 40 to communicate with each other when the discharge pressure of the mechanical feed pump 40 becomes higher than a predetermined discharge pressure. The fuel pressure is limited to a predetermined discharge pressure or less.

  The plunger pump 50 is a plunger pump that pressurizes the fuel regulated by the metering valve 60 and discharges (pumps) the fuel to the outside. The plunger pump 50 has a plunger 51 reciprocally driven based on the driving force of the crank shaft 23, a pressurizing chamber 52 whose volume is changed by the reciprocating movement of the plunger 51, and the pressurizing chamber 52 and the common rail 25 side. And a discharge valve 61 which communicates and shuts off.

  When the crankshaft 23 rotates, the plunger 51 reciprocates between the pumping top dead center and the pumping bottom dead center. Here, when the pressure in the pressurizing chamber 52 is lowered by the lowering of the plunger 51, the discharge valve 61 is closed, and the fuel is sucked into the pressurizing chamber 52 from the mechanical feed pump 40 through the adjusting valve 60. Ru. Conversely, when the pressure in the pressure chamber 52 rises due to the rise of the plunger 51 and the pressure in the pressure chamber 52 becomes higher than the threshold value, the discharge valve 61 is opened to pressurize in the pressure chamber 52. The high pressure fuel thus discharged is discharged (pumped) toward the common rail 25.

  The addition valve 15 in the above configuration can stably add and supply fuel into the exhaust pipe 13 when the pressure immediately before the addition valve P2 becomes higher than the predetermined pressure Ptrg. The predetermined pressure Ptrg is a value that varies depending on the addition valve 15 provided.

  It is assumed that the electric feed pump 21 is not present and the fuel is supplied to the addition valve 15 only by the mechanical feed pump 40. In this case, since the mechanical feed pump 40 is driven by the rotation of the crankshaft 23, when the rotational speed of the crankshaft 23 is low, the pump rotational speed of the mechanical feed pump 40 is also low, as shown in FIG. The pressure of fuel discharged by the mechanical feed pump 40 also decreases. In particular, at the pump rotational speed in a predetermined range including the pump rotational speed at idle, the pressure of the fuel supplied to the addition valve 15 by the mechanical feed pump 40 becomes lower than the predetermined pressure Ptrg. There is a risk that fuel can not be added and supplied stably inside.

  As a countermeasure, in the present embodiment, the electric feed pump 21 is provided. When the mechanical feed pump 40 can not supply sufficient fuel to the addition valve 15 and the pressure immediately before the addition valve P2 is lower than the predetermined pressure Ptrg, the pressure P2 immediately before the addition valve is smaller than the predetermined pressure Ptrg. The fuel supply assist is carried out so as to be higher.

  In the present embodiment, the ECU 30 implements supply assist control described in FIG. 4 described later. The supply assist control shown in FIG. 4 is repeatedly performed by the ECU 30 in a predetermined cycle while the ECU 30 is powered on.

First, in step S100, the rotational speed (engine rotational speed) NE of the crankshaft 23 is calculated from the rotational angle of the crankshaft 23 detected by the crank angle sensor 27. In step S110, the temperature Thf of the fuel flowing into the storage chamber 54 detected by the temperature sensor 55 is acquired. In step S120, the pressure immediately before the addition valve P2 detected by the first pressure sensor 26 is acquired.
In step S130, the bulk modulus E of the fuel is calculated based on equation (1). The bulk elastic modulus E of the fuel changes depending on the pressure P2 immediately before the addition valve and the temperature Thf.

  In step S140, a target fuel supply amount Qtrg is calculated. The target fuel supply amount Qtrg is calculated using equation (2). Specifically, a predetermined pressure Ptrg set as a pressure at which the addition valve 15 can add and supply fuel into the exhaust pipe 13, and a pipe volume Vinj from the mechanical feed pump 40 to the addition valve 15 are calculated as the volume elastic coefficient of fuel Find the product of the quotient divided by E. The calculated value corresponds to the target fuel supply amount Qtrg.

  FIG. 5 shows the fuel supply amount supplied to the addition valve 15 by the mechanical feed pump 40 which varies depending on the engine rotational speed NE. In step S150, the fuel supply amount Qmf of the mechanical feed pump 40 corresponding to the current engine rotational speed NE is acquired based on the map described in FIG.

  Then, in step S160, it is determined whether the fuel supply amount Qmf of the mechanical feed pump 40 is larger than the target fuel supply amount Qtrg, so that the addition valve 15 is exhausted only with the fuel supply amount Qmf of the mechanical feed pump 40. It is determined whether fuel can be stably added and supplied in the pipe 13. When it is determined that the fuel supply amount Qmf is larger than the target fuel supply amount Qtrg (S160: YES), this control is ended. If the fuel supply amount Qmf is smaller than the target fuel supply amount Qtrg (S160: NO), the process proceeds to step S170. In step S170, the fuel supply assist amount Qef to be supplied by the electric feed pump 21 is calculated by calculation processing described later. Then, the process proceeds to step S180, where the electric feed pump 21 is instructed to supply the fuel of the supply assist amount Qef to the addition valve 15, and the present control is ended.

  Next, the process of calculating the supply assist amount Qef performed by the ECU 30 will be described with reference to FIG. The said process is a subroutine process corresponded to step S170 of FIG.

  First, in step S200, detection values not acquired in FIG. 6 are acquired from each sensor. The differential pressure ΔPf of the fuel, which has changed before and after passing through the fuel filter 22, is acquired from the differential pressure sensor 32. Then, in step S210, the pressure Pret of the fuel flowing into the first return flow passage 29 is calculated. Specifically, a map of the pressure Pret that fluctuates depending on the engine rotational speed NE is stored, and based on the map, the pressure Pret corresponding to the current engine rotational speed NE is acquired.

  In step S220, the mechanical feed pump 40 acquires the required discharge amount Qcm to be supplied to the common rail 25 via the plunger pump 50. The required discharge amount Qcm fluctuates depending on the engine rotation speed NE and the engine load (for example, the accelerator opening). In step S230, the required injection amount Qadd of the addition valve 15 is acquired. This corresponds to the amount of reducing agent assumed to be required to reduce and remove the NOx stored in the NOx catalyst 14.

  In step S240, the flow rate reduction coefficient Kf is calculated based on equation (3). The flow rate reduction coefficient Kf is obtained by converting the amount of fuel which decreases as the fuel passes through the fuel filter 22. Therefore, the flow rate reduction coefficient Kf is calculated based on the differential pressure ΔPf of the fuel before and after passing through the fuel filter 22 detected by the differential pressure sensor 32.

  In step S250, the inflow amount Qcof of the fuel flowing into the orifice 56 is calculated based on the equation (4). The inflow amount Qcof can be calculated based on the pressure difference between the pressure of the fuel supplied from the mechanical feed pump 40 before flowing into the orifice 56 and the pressure of the fuel after passing through the orifice 56. At this time, the pressure of the fuel supplied by the mechanical feed pump 40 before flowing into the orifice 56 corresponds to the pressure P2 immediately before the addition valve, and the pressure of the fuel after passing through the orifice 56 is the fuel flowing in the first return flow path 29 Corresponds to the pressure Pret.

  In step S260, the inflow amount Qrv of fuel flowing into the regulator valve 42 is calculated based on the equation (5). Specifically, the product of a differential pressure obtained by subtracting the addition valve immediately before pressure P2 from the predetermined pressure Ptrg and a quotient obtained by dividing the pipe volume Vrv from the mechanical feed pump 40 to the regulator valve 42 by the bulk modulus E of fuel . The calculated value corresponds to the inflow amount Qrv.

  By the way, when supplying fuel to the addition valve 15 as in the present embodiment, it is assumed that various factors affect the amount of fuel supplied to the addition valve 15.

  For example, the mechanical feed pump 40 not only supplies the fuel to the addition valve 15 but also supplies the plunger pump 50 with fuel for pressure feeding to the common rail 25. Alternatively, the addition valve 15 adds fuel to the exhaust pipe 13 to reduce the amount of fuel supplied to the addition valve 15. Alternatively, when the fuel passes through the fuel filter 22 provided between the electric feed pump 21 and the mechanical feed pump 40, the pressure of the fuel may be lost before and after passing. That is, the amount of fuel supplied to the mechanical feed pump 40 may be reduced. Furthermore, the viscosity of the fuel changes with the temperature of the fuel, and the flowability of the fuel changes, which may cause fluctuation in the amount of supplied fuel. Besides, when the fuel is supplied to the storage chamber 54, the fuel passes through the orifice 56. At this time, the pressure of the fuel may be lost. That is, the amount of fuel supplied to the storage chamber 54 may be reduced. Further, since the mechanical feed pump 40 not only supplies fuel to the addition valve 15 but also supplies fuel to the regulator valve 42, it is assumed that the amount supplied to the addition valve 15 is affected.

  Therefore, in step S270, the supply assist amount Qef to be supplied by the electric feed pump 21 is calculated in consideration of the above-mentioned influence.

  As described in equation (6), the product of the sum of the fuel supply amount Qmf of the mechanical feed pump 40 and the supply assist amount Qef of the electric feed pump 21 multiplied by the flow reduction coefficient Kf is pumped from the fuel tank 20 Fuel total amount Qtotal. On the other hand, as described in equation (7), the required discharge amount Qcm to the common rail 25, the required injection amount Qadd of the adding valve 15, the inflow amount Qcof of fuel flowing into the orifice 56, and the regulator valve 42 The sum of the amount of inflowing fuel Qrv and the amount of inflowing fuel is also equal to the total amount Qtotal of fuel pumped up from the fuel tank 20. Therefore, the supply assist amount Qef of the electric feed pump 21 is organized as the equations (6) and (7). Thus, the derived equation is equation (8). The supply assist amount Qef of the electric feed pump 21 is calculated using the derived equation (8). And this control is ended.

  According to the above configuration, the present embodiment has the following effects.

  · If the pump rotational speed of the mechanical feed pump 40 is in the low rotation range and sufficient fuel can not be supplied to the addition valve 15, the fuel feed assist by the electric feed pump 21 is performed to specify the addition valve immediately before pressure P2. The pressure can be raised to Ptrg. As a result, the addition valve 15 can stably add fuel into the exhaust pipe 13.

  By calculating the supply assist amount Qef of the electric feed pump 21 using the equation (8), various factors that affect the amount of fuel supplied to the addition valve 15 can be taken into consideration. Therefore, the addition valve immediately before the addition valve P2 can be controlled more accurately to the predetermined pressure Ptrg by the supply assist by the electric feed pump 21, and the addition valve 15 can stably supply the fuel into the exhaust pipe 13. .

  The rotational speed of the mechanical feed pump 40 changes in accordance with the rotational speed NE of the engine 10. Therefore, by referring to the map shown in FIG. 5, it becomes possible to easily acquire the current fuel supply amount Qmf being supplied to the addition valve 15 by the mechanical feed pump 40.

  The first pressure sensor 26 is disposed between the mechanical feed pump 40 and the addition valve 15. Since the pressure of the fuel supplied to the addition valve 15 is directly detected by this, it is determined whether the fuel supply assist by the electric feed pump 21 is necessary and the fuel supply assist is necessary. The calculation of the supply amount to be instructed to the electric feed pump 21 can be performed with high accuracy.

  The above embodiment can be modified as follows.

  In the above embodiment, the fuel added and supplied into the exhaust pipe 13 by the addition valve 15 is used for reduction and removal of NOx stored in the NOx catalyst 14. In this regard, other reducing agents may be used for the reduction and removal of NOx, for example, urea water may be used as the reducing agent.

  In the above embodiment, the temperature sensor 55 is provided in the storage chamber 54. In this regard, the temperature sensor 55 need not necessarily be provided in the storage chamber 54, and may be provided, for example, in the first return flow passage 29.

  In the above embodiment, the NOx catalyst 14 is provided downstream of the addition valve 15. Instead of the NOx catalyst 14, a DPF (Diesel Particulate Filter) may be provided. In this case, the required injection amount Qadd is set to correspond to the amount of fuel assumed to be necessary to burn the PM collected by the DPF.

  In the above embodiment, the NOx catalyst 14 is provided downstream of the addition valve 15. In this regard, the DPF may be provided upstream of the NOx catalyst 14 and downstream of the addition valve 15. In this case, the required injection amount Qadd is a fuel amount assumed to be necessary for burning the PM collected by the DPF, and a fuel necessary for reducing and removing NOx stored in the NOx catalyst 14 It corresponds to the sum of the amount of

  In the embodiment described above, the first pressure sensor 26 is provided in the fuel supply path from the fuel pump 24 to the addition valve 15 in order to detect the pre-addition valve pressure P2. In this regard, it is not necessary to provide the first pressure sensor 26 in the fuel supply path from the fuel pump 24 to the addition valve 15. For example, a second pressure sensor 26A (see FIGS. 1 and 2) may be provided in the fuel path from the fuel filter 22 to the fuel pump 24. In this case, the pressure detected by the second pressure sensor, the pipe volume Vinj of the fuel supply path from the fuel pump 24 to the addition valve 15, and the fuel supply amount supplied to the addition valve 15 in accordance with Equations 2 and 5. And the addition valve immediately before pressure P2 can be calculated (corresponding to the immediately before pressure detection unit).

  In the above embodiment, the first pressure sensor 26 is provided in the fuel supply path from the fuel pump 24 to the addition valve 15 to detect the pressure P2 immediately before the addition valve. The detection of the pressure immediately before the addition valve P2 by the first pressure sensor 26 is slightly delayed until the pressure fluctuation etc. caused by the addition and supply of fuel from the addition valve 15 into the exhaust pipe 13 is actually detected (detection It is assumed that a delay will occur. That is, there is a possibility that the pre-addition valve pressure P2 detected by the first pressure sensor 26 is actually the pre-addition valve pressure P2 generated earlier by the detection delay time. Therefore, if the pre-addition valve pressure P2 detected by the first pressure sensor 26 is used as the current pre-addition valve pressure P2, an error occurs with the actual pressure of the fuel supplied to the addition valve 15 . Therefore, it is possible to predict and calculate the addition valve immediately before pressure P2 detected only after the detection delay time from the present time, and use the predicted addition valve immediately before pressure P2 as the current addition valve immediately before pressure P2 Equivalent to the previous pressure detection unit). In this case, it is possible to reduce an error that occurs between the fuel supplied to the addition valve 15 and the actual pressure of the fuel.

  In the above embodiment, the supply assist amount Qef to be supplied by the electric feed pump 21 is calculated on the assumption of various factors that affect the amount of fuel supplied to the addition valve 15. Regarding this, for example, a difference calculated by subtracting the fuel supply amount Qmf of the mechanical feed pump 40 from the target fuel supply amount Qtrg may be set as the supply assist amount Qef to be supplied by the electric feed pump 21. In this case, since it is not necessary to perform the subroutine process shown in FIG. 6, it is possible to simplify the process of calculating the supply assist amount Qef.

  Even if the electric feed pump 21 supplies the supply assist amount Qef calculated in the present embodiment or the above embodiment to the addition valve 15, the supply assist amount is prepared in case the pressure P2 immediately before the addition valve does not become larger than the predetermined pressure Ptrg. It is preferable to implement Qef feedback control. Specifically, the ECU 30 performs a supply assist amount feedback process described in FIG. 7 described later.

  First, in step S300, the pressure immediately before the addition valve P2 detected by the first pressure sensor 26 is acquired. Then, in step S310, the pressure deviation amount ΔP is calculated by subtracting the pressure immediately before the addition valve P2 from the predetermined pressure Ptrg, and the process proceeds to step S320.

  In step S320, it is determined whether ΔP is within a predetermined range. The predetermined range is a range for determining that ΔP substantially matches zero. If ΔP does not fall within the predetermined range (S320: NO), the process proceeds to step S330, and the correction value Qfb of the fuel supply amount is calculated by PID control so that ΔP falls within the predetermined range. Specifically, the correction value Qfb is calculated based on a proportional term, an integral term, and a differential term of ΔP. Then, the process proceeds to step S340. If ΔP falls within the predetermined range (S320: YES), the process proceeds to step S360, sets the correction value Qfb of the fuel supply amount as 0, and proceeds to step S340.

  In step S340, the correction value Qfb of the fuel supply amount calculated in step S330 or step S360 is added to the supply assist amount Qef supplied by the electric feed pump 21 calculated in the other example or the above embodiment. The corrected fuel supply amount Qf_ef of the electric feed pump 21 is calculated. In step S350, the electric feed pump 21 is instructed to supply the fuel of the corrected fuel supply amount Qf_ef to the addition valve 15, and the present control is ended. As a result, even if the fuel feed assist is performed by the electric feed pump 21 and the pressure immediately before the addition valve P2 does not reach the predetermined pressure Ptrg, or the fuel feed assist is performed by the electric feed pump 21, the addition valve It becomes possible to carry out correction of the amount of fuel supply by the electric feed pump 21 when the previous pressure P2 becomes larger than the predetermined pressure Ptrg. That is, the pressure immediately before the addition valve P2 can be more reliably controlled to the predetermined pressure Ptrg.

  In the above embodiment, the supply assist control described in FIG. 4 is performed. In this regard, the supply assist control described in FIG. 4 does not necessarily have to be performed, and for example, the supply assist control described in FIG. 8 may be performed.

  FIG. 8 is a partial modification of FIG. That is, step S415 is newly inserted between step S410 corresponding to step S210 and step S420 corresponding to step S220. In addition, step S455 is newly inserted between step S450 corresponding to step S250 and step S460 corresponding to step S260. Furthermore, after the process of step S470 corresponding to step S270, steps S480 and S490 are added.

  Step S415 is the same process as step S150 described in FIG. Step S455 is the same process as step S130 shown in FIG. Step S480 determines whether the supply assist amount Qef calculated in step S470 is larger than zero. Then, when it is determined that the supply assist amount Qef calculated in step S470 is smaller than 0 (S480: NO), this control is ended. This is because the fuel can be supplied more than the target fuel supply amount Qtrg only by the fuel supply by the mechanical feed pump 40, and the addition valve 15 can stably add the fuel to the exhaust pipe 13 . If it is determined in step S470 that the supply assist amount Qef calculated in step S470 is larger than 0 (S480: YES), the process proceeds to step S490, and the fuel of the supply assist amount Qef is supplied to the electric feed pump 21 with respect to the addition valve 15. Command to supply and complete this control.

  For the other steps, the processes of steps S400, S430, and S440 of FIG. 8 are the same as the processes of steps S200, S230, and S240 of FIG. 6, respectively.

  The effect according to the said embodiment is show | played also by this example of another.

  It is assumed that the electric feed pump 21 has a function capable of sucking back the fuel supplied to the fuel pump 24 by the reverse driving as well as sending the fuel to the fuel pump 24 by the normal rotation driving. In this case, the ECU 30 may perform reverse drive processing described in FIG. 9 described later. The reverse rotation drive process shown in FIG. 9 is repeatedly performed by the ECU 30 in a predetermined cycle while the ECU 30 is powered on.

  First, in step S500, it is determined based on the detection value detected by the first pressure sensor 26 whether or not there is an abnormality in the pressure of the fuel. For example, the detected value detected by the first pressure sensor 26 causes an unintended decrease over time. Alternatively, when the feedback control described in FIG. 7 is performed and the correction value Qfb of the fuel supply amount calculated in step S330 increases with the passage of time, the fuel supplied from the fuel tank 20 is It is determined that there is a possibility that a leak has occurred in a section of the fuel supply path, and the abnormality is determined. Alternatively, if the amount of change of the addition valve immediately before the addition valve P2 in the predetermined period is larger than the determination pressure determined to be the excessive pressure increase, it is determined that the fuel supply to the addition valve 15 is excessive.

  If it is determined that there is no abnormality in the pressure of the fuel (S500: NO), the process proceeds to step S570 described later. If it is determined that there is an abnormality in the pressure of the fuel (S500: YES), the process proceeds to step S510, and the fuel supply assist by the electric feed pump 21 is performed when the fuel supply assist by the electric feed pump 21 is performed. Stop the supply assist.

  In step S520, it is determined whether or not there is an abnormality in the pressure of the fuel regardless of stopping the fuel supply assist by the electric feed pump 21.

  If it is determined that there is no abnormality in the pressure of the fuel (S520: NO), the process proceeds to step S570 described later. If it is determined that the fuel pressure is still abnormal although the fuel supply assist by the electric feed pump 21 is stopped (S520: YES), the process proceeds to step S530.

  In step S530, it is determined whether the engine 10 is stopped. For example, it is determined that the engine 10 is stopped because the engine rotational speed NE is lower than a predetermined rotational speed. If it is determined that the engine 10 is stopped (S530: YES), the process proceeds to step S570. In step S570, cancellation processing of the suction return request by the electric feed pump 21 is performed. This is because there is no abnormality in the pressure of the fuel, or the fuel supply by the mechanical feed pump 40 is stopped by stopping the engine 10, and more fuel flows from the fuel tank 20 into the fuel supply path. It is because there is no such thing. If it is determined that the engine 10 has not stopped (S530: NO), the process proceeds to step S540, and a suction return request by the electric feed pump 21 is issued.

  In step S550, it is determined whether a suction return request by the electric feed pump 21 has been issued. When it is determined that the suction return request by the electric feed pump 21 is not issued (S550: NO), this control is ended. If it is determined that the suction return request by the electric feed pump 21 is issued (S550: YES), the process proceeds to step S560, the electric feed pump 21 is reversely driven, and the mechanical feed pump 40 is pumped up from the fuel tank 20. Suck back some fuel. And this control is ended.

  Therefore, for example, when it is determined that the fuel present in the fuel supply passage is abnormally leaking, the fuel present in the fuel supply passage including the addition valve 15 is sent to the fuel tank 20 by driving the electric feed pump 21 reversely. It is possible to return. As a result, it is possible to quickly suppress problems (such as an increase in the amount of consumption of fuel) caused by a leak of fuel occurring in the fuel supply path. Alternatively, it is assumed that the fuel supply to the addition valve 15 is determined to be excessive. In this case, since the pressure immediately before the addition valve P2 is excessively high, the fuel is injected more than the necessary amount, and the consumption amount becomes large. Therefore, even when it is determined that the fuel supply to the addition valve 15 is excessive, the electric feed pump 21 is similarly reversely driven to reduce the fuel supplied to the addition valve 15. As a result, the pressure P2 immediately before the addition valve can be reduced, and the consumption of fuel can be suppressed.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 13 ... Exhaust pipe, 14 ... NOx catalyst, 15 ... Addition valve, 20 ... Fuel tank, 21 ... Electric feed pump, 26 ... First pressure sensor, 30 ... ECU, 40 ... Mecha feed pump.

Claims (10)

A purification unit (14) disposed in an exhaust pipe (13) of the internal combustion engine (10) and purifying exhaust gas;
An addition valve (15) which is disposed upstream of the purification unit in the exhaust pipe and adds an additive for exhaust gas purification into the exhaust pipe;
A mechanical feed pump (40) driven at a rotational speed according to the rotational speed of the internal combustion engine by the driving force of the internal combustion engine to pressurize the additive and supply it to the addition valve;
A motor-driven feed pump (21) driven by a motor to pressurize the additive from the additive supply source (20) and supply the additive to the mechanical feed pump;
A pressure detection unit (26) for detecting the pressure of the additive supplied from the mechanical supply pump to the addition valve as a pressure immediately before the addition valve;
Drive unit for driving the electric supply pump so that the addition valve immediately before pressure is higher than the predetermined pressure when the pressure immediately before the addition valve detected by the immediately preceding pressure detection unit is lower than a predetermined pressure 30) and
An exhaust gas purification system comprising:   The drive unit is configured to supply the mechanical feed pump to the addition valve at present from a target supply amount as a total supply amount of the additive to the addition valve necessary for the pressure immediately before the addition valve to be the predetermined pressure. The exhaust gas purification system according to claim 1, wherein a supply assist amount obtained by subtracting an actual supply amount as a supply amount of the present additive being supplied is supplied by the electric supply pump.   The drive unit has a map representing the relationship between the rotational speed of the internal combustion engine and the supply amount of the additive supplied by the mechanical supply pump to the addition valve, and the present portion can be obtained by referring to the map. The exhaust gas purification system according to claim 2, wherein the actual supply amount at the rotational speed is acquired. The additive is a fuel,
The internal combustion engine is
An accumulator (25) for storing the fuel under high pressure;
A high pressure pump (50) for pressure-feeding the fuel supplied from the mechanical supply pump to the pressure accumulation container;
Equipped with
The exhaust gas purification system
A filter (22) for collecting foreign matter in the fuel, between the electric supply pump and the mechanical supply pump;
A temperature detection unit (55) for detecting the temperature of the fuel supplied by the mechanical supply pump;
Equipped with
The drive unit includes an amount of outflow of the fuel flowing out from the mechanical supply pump, an amount of supply of the fuel supplied from the mechanical supply pump to the high pressure pump, and a quantity of the fuel injected by the addition valve. The supply assist amount is calculated in consideration of the injection amount, the first pressure loss generated when the fuel is passed through the filter, and the temperature detected by the temperature detection unit. The exhaust gas purification system of any one of claim 2 or 3. The exhaust gas purification system includes a return flow path (29, 33) for returning the part of the fuel out of the fuel flowing out of the mechanical supply pump upstream of the mechanical supply pump;
The drive unit is characterized in that a supply assist amount as a supply amount to be supplied by the electric supply pump is calculated by further considering an outflow amount of the fuel flowing out from the mechanical supply pump into the return flow path. The exhaust gas purification system according to claim 4.   When the pressure of the additive supplied from the mechanical supply pump to the addition valve changes, the drive unit detects the pressure immediately before the addition valve detected by the immediately preceding pressure detection unit along with the change. The exhaust gas purification system according to any one of claims 1 to 5, wherein the present immediately preceding addition valve pressure is predicted and calculated in consideration of a detection delay up to the time when a fluctuation occurs.   The drive unit feedback-controls the supply amount of the additive supplied from the electric supply pump to the mechanical supply pump such that the pressure immediately before the addition valve becomes the predetermined pressure. An exhaust gas purification system according to any one of 1 to 6. The motorized feed pump can be driven in reverse.
When the drive unit determines that the fuel supplied from the mechanical supply pump is leaking abnormally, or the pressure supplied from the mechanical supply pump is higher than a determination pressure determined to be an overpressure. The exhaust gas purification system according to any one of claims 1 to 7, wherein the electric supply pump is reversely driven when it is determined that the pressure of the valve is high. A first pressure sensor (26) disposed between the mechanical supply pump and the addition valve for detecting the pressure of the additive flowing from the mechanical supply pump into the addition valve;
The exhaust gas purification system according to any one of claims 1 to 8, wherein the immediately preceding pressure detection unit acquires the pressure detected by the first pressure sensor as the immediately preceding addition valve pressure. A second pressure sensor (26A) disposed between the mechanical supply pump and the electric supply pump for detecting the pressure of the additive flowing from the electric supply pump to the mechanical supply pump;
The immediately preceding pressure detection unit includes the pressure detected by the second pressure sensor, the flow rate of the additive flowing to the addition valve, and the volume in the additive inflow path from the mechanical supply pump to the addition valve. 10. The exhaust gas purification system according to any one of claims 1 to 9, wherein the pressure immediately before the addition valve is calculated based on.

Images