JP2009209809A - Supercharging device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means capable of restraining an increase in a generation quantity such as NOx and soot, when increasing fuel injection quantity for preventing reduction in an engine speed, when starting a vehicle. <P>SOLUTION: A diesel engine E has an exhaust turbocharger 19 and an electric supercharger 21 as a supercharging device. and premixes and burns fuel, by supplying EGR gas in large quantities by quickening the fuel injection timing, more than the compression top dead center in a premix combustion region. While in a diffusion combustion region, the fuel is burned diffusively by setting the fuel injection timing in the vicinity of the compression top dead center. In an engine E, when the engine speed is reduced when starting the vehicle, the electric supercharger 21 is operated; and the valve closing timing of an intake valve 1 is delayed; the furl injection timing is advanced; and premix combustion of the fuel is performed. Thus, even when the fuel injection quantity is increased, when starting the vehicle, an increase in the generation quantity, such as, NOx and soot can be restrained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine supercharger including an exhaust turbocharger and an electric supercharger.

  Diesel engines are widely used as engines for automobiles because of their high thermal efficiency and good fuel economy, so they can reduce CO2 emissions, which contribute to global warming, and they have high durability and reliability. It has been. On the other hand, since exhaust gas from diesel engines contains air pollutants such as NOx (nitrogen oxide) and soot, in recent years, it has been required to significantly reduce these air pollutants. Note that the amount of NOx generated increases when the combustion temperature of the fuel in the combustion chamber is high.

Therefore, by introducing a relatively large amount of EGR gas into the combustion chamber in the low output region, the fuel injection timing is advanced from the compression top dead center, and the fuel is premixed and combusted at a relatively low temperature (hereinafter, this region is referred to as “combustion combustion”). A diesel engine that reduces the amount of NOx and soot generated has been proposed (for example, see Patent Document 1). Even in a diesel engine that performs premixed combustion in this way, in a region other than the low-power region (high-power region), fuel is injected near the compression top dead center in the same manner as an ordinary diesel engine, and diffusion combustion is performed. (This region is hereinafter referred to as “diffusion combustion region”).
JP 2001-82233 A (paragraph [0057], FIG. 8)

  By the way, in general, when the vehicle starts, the engine rotational speed may decrease and the rotational stability of the engine may be temporarily impaired. Especially in such a manual transmission vehicle, an engine stall (engine stall) is caused when the clutch is connected. There is a risk of it happening. On the other hand, when the engine speed decreases to a predetermined value or less at the start of the vehicle, it can be considered that the engine speed is increased by increasing the fuel injection amount to increase the rotational stability of the engine. However, when the fuel injection amount is increased in this way at the start of the vehicle, the amount of air pollutants such as NOx and soot at the start of the vehicle increases, resulting in a problem that the emission performance decreases.

  The present invention has been made to solve the above-described conventional problems, and when starting a vehicle equipped with a diesel engine, when the fuel injection amount is increased to prevent a decrease in the engine speed, the NOx It is an object to be solved to provide means that can effectively prevent or suppress an increase in the amount of air pollutants such as soot.

  An engine supercharging device according to the present invention made to solve the above problems includes: (a) an exhaust turbocharger; (b) an intake passage upstream of a compressor of the exhaust turbocharger; An exhaust passage downstream of the turbocharger turbine and connected to the exhaust passage (as EGR gas) to recirculate part of the exhaust gas in the exhaust passage; and (c) the EGR passage, An EGR valve that adjusts (or controls) the recirculation state of exhaust gas; and (d) an air flow rate (or pressure) in the intake passage that is disposed in the intake passage upstream of the connection portion between the EGR passage and the intake passage. An intake control valve for controlling the engine, (e) an electric supercharger disposed in the intake passage, (f) an electric supercharger control means for controlling the operation of the electric supercharger, and (g) when the vehicle starts The engine speed is a preset reference value (hereinafter referred to as “fuel increase rotation And a fuel increasing means for increasing the amount of fuel injected into the engine when it decreases to (h) an intake control when the operating state of the engine is in a preset premixed combustion region. And a premixed combustion control means for controlling the valve and the EGR valve so that the exhaust gas recirculates (to the extent that premixed combustion is possible) and advancing the fuel injection timing to perform premixed combustion.

  In this engine supercharging device, the electric supercharger control means operates the electric supercharger when the engine speed drops below the fuel increase speed when the vehicle starts. Further, the premixed combustion control means is configured to perform premixed combustion when the engine speed decreases to a fuel increase speed or less when the vehicle starts.

  In the engine supercharging device according to the present invention, when the intake valve control means for controlling the opening and closing timing of the intake valve is provided, the intake valve control means retards the closing timing of the intake valve when the vehicle starts. It is preferred that

  Further, in the engine supercharging device according to the present invention, the electric supercharger control means preliminarily drives the electric supercharger at a speed lower than the normal operating speed at the time when the start of the clutch operation is detected when the vehicle starts. It is preferable that the electric supercharger is operated at the normal operation speed when the engine speed is decreased to a fuel increase speed or less after the clutch operation is started.

  According to the engine supercharging device of the present invention, premixed combustion is performed when the vehicle starts, so that the fuel combustion temperature can be lowered, and the amount of NOx and soot generated can be reduced even if the fuel injection amount is increased. The increase can be prevented or suppressed. Furthermore, since the electric supercharger is operated when the vehicle starts, the mixing property or mixing property of fresh air and EGR gas in the premixed combustion is improved. Thereby, a mixture of fresh air and EGR gas can be supplied to the combustion chamber with good responsiveness. For this reason, premixed combustion can be performed appropriately and reliably when the vehicle starts, and the emission performance can be improved.

  In the engine supercharging device according to the present invention, when the closing timing of the intake valve is retarded when the vehicle starts, the effective compression ratio can be lowered, and the fuel self-ignites in premixed combustion. The period until it can be extended. For this reason, a sufficient mixing period of fuel and air or EGR gas can be ensured, premixed combustion can be performed more reliably and appropriately at the start of the vehicle, and emission performance can be improved more effectively.

  In the engine supercharging device according to the present invention, when the electric supercharger is operated in advance at a low rotational speed when the start of clutch operation is detected, the electric supercharger is operated at the time of starting the vehicle to perform supercharging. The delay in operation of the electric supercharger during the operation can be suppressed or shortened, premixed combustion at the start of the vehicle can be performed more reliably and appropriately, and the emission performance can be further enhanced.

  Hereinafter, embodiments of the present invention (best mode for carrying out the present invention) will be described in detail with reference to the accompanying drawings. FIG. 1 shows a system configuration of a direct injection type diesel engine E (hereinafter referred to as “engine E” for short) provided with a supercharging device according to the present invention. In this premixed combustion region, fuel efficiency is improved by introducing a relatively large amount of EGR gas into the intake system and injecting fuel before compression top dead center to perform premixed combustion. The amount of emission of air pollutants such as NOx and soot (smoke) is reduced. On the other hand, in the diffusion combustion region, the engine output is sufficiently increased by injecting fuel near the compression top dead center to cause diffusion combustion. The engine E is a multi-cylinder (for example, four cylinders, six cylinders, etc.) engine, but only one cylinder is shown in FIG. 1, and the other cylinders are not shown.

  As shown in FIG. 1, in the engine E, when the intake valve 1 is opened, fuel combustion air is sucked into the combustion chamber 3 from the intake port 2 (hereinafter, this air is referred to as “intake air”). That said.) Then, the intake air in the combustion chamber 3 is compressed by the piston 4 to be in a high temperature / high pressure state. Then, fuel (light oil or the like) is injected into the combustion chamber 3 from the fuel injection valve 5 before the compression stroke top dead center (premixed combustion) or near the compression stroke top dead center (diffusion combustion). Self-ignites and burns. Gas generated by combustion, that is, exhaust gas, is discharged to the exhaust port 7 when the exhaust valve 6 is opened. Although not shown, the fuel is supplied from the fuel tank to the fuel injection valve 5 through the common rail at a high pressure.

  A series of these operations is repeated, and the piston 4 repeats reciprocating motion in the cylinder axial direction within the cylinder 8. The reciprocating motion of the piston 4 is converted into a rotational motion (torque) of the crankshaft 10 by a link mechanism including a connecting rod 9, a crank arm (not shown), a crankpin (not shown), and the like. The rotational motion of the crankshaft 10 is taken out as engine output and drives a vehicle equipped with the engine E (not shown) but also drives auxiliary equipment such as an alternator and an air conditioner. The engine E is driven (cranked) by the engine starter 11 at the time of starting. Although not shown, the driving force of the crankshaft 10 is transmitted to driving wheels via a transmission, a final gear, and the like.

  In the engine E, the intake valve 1 is opened and closed by the intake valve opening / closing cam mechanism 12 at a predetermined timing. An electromagnetic intake valve cam control device 13 is provided for the intake valve opening / closing cam mechanism 12. The intake valve cam control device 13 can advance or retard the opening / closing timing of the intake valve 1 via the intake valve opening / closing cam mechanism 12 in accordance with a control signal from the control unit C. On the other hand, the exhaust valve 6 is opened and closed by the exhaust valve opening / closing cam mechanism 14 at a predetermined timing. An electromagnetic exhaust valve cam control device 15 is provided for the exhaust valve opening / closing cam mechanism 14. The exhaust valve cam control device 15 can advance or retard the opening / closing timing of the exhaust valve 6 via the exhaust valve opening / closing cam mechanism 14 in accordance with a control signal from the control unit C.

  In the engine E, the intake valve opening / closing cam mechanism 12 and the exhaust valve opening / closing cam mechanism 14 each have a constant valve opening period regardless of the advance angle / delay angle of the opening / closing timing, and the valve opening timing and the valve closing timing are the same. It is of a type that is advanced or retarded by an amount. However, the intake valve opening / closing cam mechanism 12 and the exhaust valve opening / closing cam mechanism 14 of the type in which the valve opening timing and the valve closing timing are individually advanced or retarded (that is, the valve opening period is variable) may be used. . The structure of the intake valve opening / closing cam mechanism 12 and the exhaust valve opening / closing cam mechanism 14 of any type is well known to those skilled in the art, and a detailed description thereof will be omitted.

  The intake system (intake system) that supplies intake air to the combustion chamber 3 of each cylinder of the engine E is provided with a single common intake passage 16 that is common to all cylinders. The front end (upstream end) of the common intake passage 16 is opened to the atmosphere, and an air cleaner (not shown) that removes dust and the like in the intake air sequentially from the upstream side in the flow direction of the intake air near the front end. And an air flow sensor 17 (see FIG. 3).

  Further, in the common intake passage 16, electromagnetic intake control in which the valve opening degree (that is, the cross-sectional area of the common intake passage 16) is controlled by the control unit C in order from the upstream side in the intake air flow direction. A valve 18, a compressor 19 a of the exhaust turbocharger 19, and an air-cooled intercooler 20 are provided. Here, the intake control valve 18 restricts the flow of intake air flowing through the common intake passage 16 and controls the flow rate or pressure thereof. The compressor 19a (exhaust turbocharger 19) supercharges the engine E by pressurizing and compressing the intake air. Further, the intercooler 20 cools the intake air whose temperature has increased due to pressurization and compression.

  The common intake passage 16 branches into a first branch intake passage 16a and a second branch intake passage 16b on the downstream side of the intercooler 20, and both the branch intake passages 16a and 16b are gathered slightly downstream from the branch portion to be simply separated. One common intake passage 16 is formed. An electric supercharger 21 that is rotationally driven by an electric motor is provided in the first branch intake passage 16a. The specific configuration of the electric supercharger 21 will be described later (see FIG. 2). On the other hand, the second branch intake passage 16b is provided with a check valve 22 for opening and closing the second branch intake passage 16b. Here, the check valve 22 closes the second branch intake passage 16b when the electric supercharger 21 is driven, and opens the second branch passage 16b when the electric supercharger 21 is stopped.

  The downstream end of the common intake passage 16 is connected to a surge tank 23 that attenuates the pulsation of the intake air and stabilizes the flow at the downstream side of the gathering portion of the first branch intake passage 16a and the second branch intake passage 16b. ing. A plurality of independent intake passages 24 for supplying intake air individually to the combustion chambers 3 of the respective cylinders are connected to the surge tank 23, and the downstream ends of these independent intake passages 24 are respectively connected to the intake ports 2 of the corresponding cylinders. It is connected. The surge tank 23 is provided with an intake pressure sensor 25 that detects the pressure of intake air.

  Further, the engine E is provided with an exhaust system (exhaust system) that exhausts exhaust gas discharged from each combustion chamber 3 into the atmosphere, and this exhaust system has a single common exhaust passage common to each cylinder. 26 is provided. However, in the exhaust gas flow direction, in the vicinity of the upstream end (exhaust manifold), the exhaust system is branched for each cylinder and connected to the exhaust port 7 of the corresponding cylinder. The common exhaust passage 26 is provided with a turbine 19b of an exhaust turbocharger 19 driven by exhaust gas.

  The exhaust turbocharger 19 is a variable turbocharger (VGT) that can change the passage cross-sectional area of the exhaust gas to the turbine 19b by a large number of movable flaps 27. These flaps 27 are controlled by a flap actuator 28. Then, the control unit C controls the supercharging pressure of the turbine 19b (exhaust turbocharger 19) by changing the passage cross-sectional area of the exhaust gas via the flap actuator 28 and the flap 27.

  Further, in the common exhaust passage 26, an exhaust gas purification catalyst 30 (DOC) that contains an oxidation catalyst and purifies exhaust gas and soot (particulate) are collected downstream of the turbine 19b in the exhaust flow direction. A particulate filter 31 (DPF) is provided. The exhaust gas purification catalyst 30 and the particulate filter 31 are accommodated in one casing 32 having heat resistance. The soot collected in the particulate filter 31 is appropriately expanded, for example, in an operating state in which the exhaust gas purification catalyst 31 is heated when the differential pressure before and after the particulate filter 31 exceeds a set value. It is removed by performing fuel injection in the stroke and burning it.

  A first temperature sensor 33 and a second temperature sensor 34 are provided slightly upstream and slightly downstream of the particulate filter 31 in the exhaust gas flow direction, respectively. Further, the common exhaust passage 26 is provided with an exhaust on-off valve 35 for opening and closing the common exhaust passage 26 on the downstream side of the particulate filter 31 or the second temperature sensor 34. The valve opening degree of the exhaust opening / closing valve 35 (that is, the passage sectional area of the common exhaust passage 26) is controlled by the control unit C.

  Furthermore, the engine E has a relatively low pressure and a relatively low temperature (turbine) downstream of the particulate filter in the common exhaust passage 26 (downstream of the turbine) for the main purpose of reducing the amount of NOx generated due to fuel combustion. An EGR device 41 is provided that recirculates part of the exhaust gas (as compared to the exhaust gas upstream of 19b) to the intake system as EGR gas. The EGR device 41 is provided with an EGR passage 42 serving as an EGR gas flow path. Here, the upstream end of the EGR passage 42 as viewed in the EGR gas flow direction is connected to the common exhaust passage 26 at a portion between the particulate filter 31 and the exhaust on-off valve 35. On the other hand, the downstream end of the EGR passage 42 as viewed in the EGR gas flow direction is connected to the common intake passage 16 at a portion between the intake control valve 18 and the compressor 19a.

  In the EGR passage 42, an air-cooled EGR cooler 43 that cools the EGR gas in order from the upstream side in the flow direction of the EGR gas, and the exhaust gas recirculation state or the recirculation amount, that is, the supply amount of the EGR gas is adjusted. An EGR control valve 44 (EGR valve) to be controlled is provided. Another EGR device that recirculates a part of the relatively high pressure and relatively high temperature exhaust gas upstream of the turbine 19b in the common exhaust passage 26 to the intake system (for example, the surge tank 23) downstream of the compressor 19a as EGR gas. May be provided.

  Next, a specific configuration of the electric supercharger 21 will be described with reference to FIG. As shown in FIG. 2, the electric supercharger 21 pressurizes the intake air sucked in from the suction port 46 in the direction indicated by the arrow A1, and discharges it from the discharge port 47 in the direction indicated by the arrow A2. 48 and an electric motor unit 49 that is integrally formed with the compressor unit 48 and that rotationally drives the compressor unit 48. Although not shown, a voltage control unit is provided in the motor unit 49. This voltage control unit boosts the power supplied from the battery (not shown) to the motor unit 49. That is, although the battery voltage is approximately 12V, it is inefficient to drive the motor unit 49 at 12V. In this electric supercharger 21, the voltage control unit boosts the battery voltage of 12V to 24V. Thus, the current value is amplified to increase the efficiency.

  The motor unit 49 is provided with a cooling water jacket 50 for cooling the motor unit 49 and the voltage control unit with cooling water. That is, the electric supercharger 21 is a water cooling type. As described above, since the motor unit 49 incorporating the voltage control unit is cooled by the cooling water, the motor unit 49 or the voltage control unit can be effectively cooled, and its durability or reliability. Can be increased. The electric supercharger 21 may be an air-cooled electric supercharger that dissipates heat by cooling fins.

  As shown in FIG. 3, the engine E is provided with various sensors for collecting various information related to the operating state. That is, in addition to the air flow sensor 17, the intake pressure sensor 25, the first temperature sensor 33, and the second temperature sensor 34, an engine speed sensor 51 that detects the rotation speed (engine speed) of the crankshaft 10, A crank angle sensor 52 that detects the crank angle, an engine water temperature sensor 53 that detects the coolant temperature of the engine E (engine water temperature), an accelerator opening sensor 54 that detects the opening of the accelerator pedal (accelerator opening), An intake air temperature sensor 55 for detecting the temperature and a clutch sensor 56 for detecting whether or not a clutch pedal (not shown) is operated or depressed are provided. Detection signals from these sensors are input to the control unit C as control information for the engine E and the like.

  The control unit C is an engine including “electric supercharger control means”, “fuel increase means”, “premixed combustion control means” and “intake valve control means” described in the section for solving the problem. E or a comprehensive control means for the attached device. Although not shown in detail, the control unit C performs an input / output unit (interface) for inputting / outputting control signals, a storage unit (ROM, RAM, etc.) for storing data and control information, and various arithmetic processes. A computer including a central processing unit (CPU), a timer counter, and the like.

  And the control unit C is based on the various data detected by each said sensor, the fuel injection valve 5, the intake valve cam control apparatus 13, the exhaust valve cam control apparatus 15, the intake control valve 18, the electric supercharger 21, By controlling or driving the check valve 22, flap actuator 28, exhaust opening / closing valve 35, EGR control valve 44, etc., normal engine control such as fuel injection amount control, boost pressure control, particulate filter 31 regeneration control, etc. Is supposed to do. Further, the control unit C includes engine control (hereinafter referred to as convenience) including drive control of the electric supercharger 21, EGR control, valve closing timing control of the intake valve 1, and fuel injection timing change control. "Electric supercharger control"). However, the control method for ordinary engine control is well known to those skilled in the art, and since such ordinary engine control is not the gist of the present invention, the description thereof is omitted.

  Hereinafter, the control procedure of the electric supercharger control according to the present invention executed by the control unit C will be described in detail with reference to the flowchart shown in FIG. In the present embodiment, the vehicle equipped with the engine E is a manual transmission vehicle, but the present invention can of course be applied to an engine mounted on an automatic transmission vehicle. As shown in FIG. 4, in this electric supercharger control, when the control is started (start), first, in step S1, the physical property values or the values detected by the sensors 17, 25, 33, 34, 51-56. Various signals corresponding to the detected values are read.

  Next, in step S2, based on the engine water temperature detected by the engine water temperature sensor 53, it is determined whether or not the engine E is in a warm state (for example, the engine water temperature is 60 ° C. or higher or 70 ° C. or higher). . If it is determined that the engine E is in a warm state (YES), it is further determined in step S3 whether or not the clutch has been operated, that is, whether or not the clutch pedal has been depressed, based on the detection value of the clutch sensor 56. Determined. If it is determined that there has been a clutch operation (YES), it is determined in step S4 whether the vehicle is starting based on the accelerator opening detected by the accelerator opening sensor 54 or the rate of change with respect to that time. Is done. For example, when the gear position is the first speed (low) and the accelerator pedal is opened from the fully closed state, it is determined that the vehicle is starting.

  If it is determined in step S4 that the vehicle is starting (YES), steps S5 to S11 are executed. That is, in steps S2 to S4, steps S5 to S11 are executed only when it is determined that the engine E is in the warm state, the clutch is operated, and the vehicle is starting, and the electric power for starting the vehicle is obtained. Supercharger control is performed. In other cases (any one of steps S2 to S4 is NO), steps S12 to S17 are executed, and electric supercharger control for normal time (except when the vehicle starts) is performed.

  Hereinafter, the electric supercharger control for starting the vehicle in steps S5 to S11 will be described. In this case, first, in step S5, the electric supercharger 21 is pre-rotated (operated) at a preset rotational speed (for example, 1000 to 2000 rpm) lower than a normal operating rotational speed (for example, 50000 to 70000 rpm). It is done. Thus, the pre-rotation of the electric supercharger 21 is to suppress the operation delay of the electric supercharger 21 when the electric supercharger 21 is operated at a normal operation rotational speed in step S9 described later. This is because the premixed combustion at the time of start of the vehicle is surely and appropriately performed.

  Next, in step S6, it is determined whether or not the engine speed detected by the engine speed sensor 51 is equal to or less than a preset fuel increase speed α. This fuel increase rotational speed α is set to a rotational speed at which the rotational stability of the engine E is impaired when the engine rotational speed decreases below this, that is, a rotational speed at which engine stall may occur in a manual transmission vehicle. Specifically, the fuel increase speed α is set to an engine speed slightly lower than the idle speed, for example, 350 to 400 rpm. Here, if it is determined that the engine speed exceeds the fuel increase speed α (NO), it is not necessary to increase the engine speed by increasing the fuel, so the following steps S7 to S11 are skipped. The process returns to step S1 (return).

  On the other hand, if it is determined in step S6 that the engine speed is equal to or lower than the fuel increase speed α (YES), step S7 is performed in order to restore the rotational stability of the engine E or prevent the engine stall. As a result, the fuel injection amount is increased. Subsequently, in step S8, the excess air ratio λ is controlled by adjusting the opening of the intake control valve 18, while the EGR control valve 44 is fully opened. Thereby, the flow rate of intake air and the recirculation amount of exhaust gas (EGR gas supply amount) are in a state suitable for premixed combustion. In addition, the control method of the normal premixed combustion in step S13 described later can be applied to the premixed combustion at the time of starting the vehicle.

  Next, in step S9, the electric supercharger 21 is operated at a normal operation speed (for example, 50000 to 70000 rpm). In this way, since the electric supercharger 21 is operated when the vehicle starts, the intake air and the EGR gas (exhaust gas) can be suppressed or shortened to suppress or shorten the delay in the supply of the intake air with respect to the increase in the fuel injection amount. ) Gas mixture (hereinafter referred to as “exhaust mixed intake air”) can be supplied to the combustion chamber 3, and the mixing property or mixing property of the intake air and the EGR gas can be improved. Thereby, the premixed combustion in step S11 described later can be performed properly.

  Thereafter, in step S10, whether or not the intake pressure (intake air pressure) detected by the intake pressure sensor 25 is equal to or higher than a predetermined set pressure β, that is, supercharging by the electric supercharger 21 is appropriately performed. It is determined whether or not This set pressure β is set to a pressure (for example, 100 to 120 kPa) that becomes an intake pressure suitable for premixed combustion when the vehicle starts when the intake pressure becomes higher than this. If it is determined that the intake pressure is less than the set pressure β (NO), the intake pressure has not yet reached a pressure suitable for premixed combustion, so step S11 is skipped and step S1 is skipped. Return to (Return).

  On the other hand, if it is determined in step S10 that the intake pressure is equal to or higher than the set pressure β (YES), since the intake pressure is already suitable for premixed combustion, the intake valve 1 is determined in step S11. Is closed by a predetermined angle (for example, a crank angle of 20 to 40 °), and the fuel injection timing is advanced by a predetermined angle (for example, a crank angle of 60 to 70 °). Mixed combustion is performed. Here, retarding the valve closing timing of the intake valve 1 lowers the effective compression ratio, lengthens the period until the fuel self-ignites in the premixed combustion, and ignites the fuel near the compression top dead center. This is to cause appropriate premixed combustion. As a result, a sufficient mixing period of fuel and air or EGR gas can be secured, premixed combustion can be performed reliably and appropriately at the start of the vehicle, and emission performance can be effectively enhanced.

  Hereinafter, the control procedure of the electric supercharger control for normal time (except when the vehicle starts) in steps S12 to S17 will be described. If it is determined in step S2 that the engine E is in a warm state (YES), and it is determined in step S3 that there is no clutch operation (NO) or it is determined in step S4 that the vehicle is not starting ( NO), it is determined in step S12 whether or not the engine operating state is in the premixed combustion region. If it is determined that the vehicle is in the premixed combustion region (YES), premixed combustion is performed in step S13, while if it is determined that the premixed combustion region is not entered (NO), step S13 is performed. In S14, diffusion combustion is performed. If it is determined in step S2 that the engine E is not in a warm state (NO), that is, if it is determined that the engine E is in a cold state, it is difficult to perform premixed combustion appropriately and reliably. Therefore, regardless of the operating state of the engine E, diffusion combustion is performed in step S14.

  FIG. 5 is a diagram showing the operation region of the engine E in a two-dimensional coordinate system in which the engine speed and the engine load are parameters (or independent variables). In this engine E, in the premixed combustion region shown in FIG. 5, a relatively large amount of EGR gas is supplied to the intake system and fuel is supplied before the compression top dead center (for example, before the compression top dead center at the crank angle). 60 to 70 °) and premixed combustion is performed. On the other hand, in the diffusion combustion region shown in FIG. 5, that is, the region other than the premixed combustion region, the fuel is injected near the compression top dead center to cause diffusion combustion. Note that L in FIG. 5 indicates the full load state.

  FIG. 6 shows that a general diesel engine has a relatively large amount of CO, HC, soot or NOx in a two-dimensional coordinate system using the local combustion temperature of fuel and the local equivalence ratio (reciprocal of excess air ratio) as parameters. It is the figure which showed the area | region which generate | occur | produces. As is apparent from FIG. 6, CO and HC are generated mainly in the low temperature / high equivalence ratio region, soot is generated mainly in the high temperature / high equivalence ratio region, and NOx is generated mainly in the high temperature / low equivalence ratio region. Between the region where much CO and HC are generated and the region where much soot is generated and the region where much NOx is generated, there is a gap region where the generation amount of CO, HC, soot and NOx is small.

  Therefore, in the engine E according to the present invention, when premixed combustion is performed, the intake air amount, the fuel injection amount, the EGR gas supply amount, the fuel so that the combustion state of the fuel enters the region P within the gap region. The injection timing is adjusted or controlled. Specifically, during premixed combustion, a relatively large amount of EGR gas is supplied to the intake system, and the combustion temperature of the fuel is lowered to suppress the generation of NOx. Further, by supplying EGR gas that is relatively low temperature and cooled by the intercooler 20 by the EGR device 41, the temperature of the exhaust mixed intake air supplied to the combustion chamber 3 is lowered, the density is increased, and the like. The quantity ratio is reduced (the excess air ratio is increased) to suppress the generation of HC, CO and soot. In other words, premixed combustion involves burning a large amount of EGR and early injection timing to burn fuel and air, which are almost equivalently mixed with a spark ignition engine (for example, a gasoline engine), at a low temperature, mainly generating NOx and soot. It suppresses.

  Thus, when premixed combustion is performed in step S13, the opening degree of the intake control valve 18 and the opening of the EGR control valve 44 are set so that the oxygen concentration of the exhaust mixed intake air supplied to the combustion chamber 3 becomes the target oxygen concentration. The degree is controlled. This control is performed by the following procedure. That is, for example, using a map having parameters of the fuel injection amount and the oxygen concentration of exhaust mixed intake air (mixed gas of intake air and EGR gas) as shown in FIG. 7, first, the engine speed (engine speed) and Based on the fuel injection amount, the target oxygen concentration of the exhaust mixed intake air is set. Then, the oxygen concentration is predicted based on a preset model. Then, based on the set target oxygen concentration and the predicted oxygen concentration, the intake control valve 18 and the EGR control valve 44 are controlled so that the oxygen concentration becomes the target value.

  Further, for example, using a map having the fuel injection amount and the excess air ratio as parameters as shown in FIG. 8, the target excess air ratio is set based on the engine speed and the fuel injection amount, and subsequently set. The intake control valve 18, the EGR control valve 44, and the exhaust turbo supercharger 19 (flap actuator 28) are controlled so as to achieve the target excess air ratio. In this way, by reducing the local temperature in the combustion chamber 3 by recirculating a large amount of exhaust gas to the intake system (supplying EGR gas), the generation of NOx is suppressed and the exhaust gas is supplied to the combustion chamber 3. By cooling the exhaust mixed intake air and increasing its density, a high excess air ratio is realized, and the occurrence of locally low temperature (T <1500 ° K) and excessively rich (φ> 1) is avoided. , HC and CO are suppressed. And by cooling the exhaust mixed intake air and supplying the EGR gas, the necessary ignition delay is ensured to suppress the generation of soot, and the excess air ratio is kept high, so that the soot generated in the middle stage of combustion is combusted. It is oxidized in the later stage to prevent soot discharge.

  On the other hand, when diffusion combustion is performed in step S14, the intake control valve 18 is fully opened while the EGR control valve 44 is fully closed. That is, in such a high output region of the engine E, in order to increase the engine output as much as possible, the intake control valve 18 is fully opened to increase the intake air amount as much as possible, and the EGR gas containing almost no oxygen. Is stopped, and as much oxygen as possible is supplied to the combustion chamber 3. The fuel injection timing is set near the compression top dead center, and the engine output is increased as much as possible by diffusing and burning the fuel.

  After performing premixed combustion or diffusion combustion in this way, it is determined in step S15 whether or not the engine E (or vehicle) is in an acceleration state based on the accelerator opening or the speed of increase. When the accelerator pedal is depressed and the engine E starts accelerating, a time delay of the intake air pressure rise (supercharging) by the exhaust turbocharger 19 with respect to the depression operation of the accelerator pedal, a so-called turbo lag occurs. Intake air is insufficient. Therefore, in the engine E, when the engine E is in an acceleration state, the electric supercharger 21 is driven to assist the increase (supercharging) of the intake air pressure so as to prevent or suppress the generation of the turbo lag. ing.

  If it is determined in step S15 that the engine E is in an accelerated state (YES), in step S16, the electric supercharger 21 is operated at a normal operation speed (for example, 50,000 to 70000 rpm), but a check is not performed. The valve 22 is closed. In this case, the intake air is quickly pressurized by the electric supercharger 21 and the generation of turbo lag is prevented or suppressed. Thereafter, the process returns to step S1 (return). On the other hand, if it is determined in step S15 that the engine E is not in an accelerated state (NO), the electric supercharger 21 is stopped and the check valve 22 is opened in step S17. In this case, the intake air bypasses the electric supercharger 21 and flows via the second branch intake passage 16b. Thereafter, the process returns to step S1 (return).

  As described above, according to the engine E according to the embodiment of the present invention, premixed combustion is performed when the vehicle starts, so that the fuel combustion temperature can be lowered, and even if the fuel injection amount is increased, NOx and soot are reduced. An increase in the generation amount can be effectively prevented or suppressed, and the emission performance can be improved. Furthermore, since the electric supercharger 21 is operated when the vehicle starts, the mixing property or mixing property of fresh air and EGR gas in the premixed combustion is improved. Thereby, a mixture of fresh air and EGR gas can be supplied to the combustion chamber with good responsiveness. For this reason, premixed combustion can be performed appropriately when the vehicle starts, and the emission performance can be improved.

It is a mimetic diagram showing the system configuration of the diesel engine provided with the supercharging device concerning the present invention. It is a side view of the electric supercharger of the engine shown in FIG. It is a block diagram which shows the structure of the control system of the engine shown in FIG. It is a flowchart which shows the control procedure of electric supercharger control of the diesel engine shown in FIG. It is the figure which represented the driving | running area | region of the diesel engine shown in FIG. 1 by the two-dimensional coordinate system which uses an engine speed and an engine load as parameters. It is the figure which showed the area | region where CO, HC, soot, or NOx generate | occur | produces comparatively much in the two-dimensional coordinate system which uses the local combustion temperature and local equivalence ratio of a parameter as parameters. It is a figure which shows the map for setting the target oxygen concentration which uses as parameters the fuel injection amount and the oxygen concentration of exhaust-mixed intake air. It is a figure which shows the map for setting the target excess air ratio which uses a fuel injection amount and an excess air ratio as parameters.

Explanation of symbols

  E diesel engine, C control unit, 1 intake valve, 2 intake port, 3 combustion chamber, 4 piston, 5 fuel injection valve, 6 exhaust valve, 7 exhaust port, 8 cylinder, 9 connecting rod, 10 crankshaft, 11 engine starter , 12 Intake valve opening / closing cam mechanism, 13 Intake valve cam control device, 14 Exhaust valve opening / closing cam mechanism, 15 Exhaust valve cam control device, 16 Common intake passage, 16a First branch intake passage, 16b Second branch intake passage, 17 Air flow Sensor, 18 Intake control valve, 19 Exhaust turbocharger, 19a Compressor, 19b Turbine, 20 Intercooler, 21 Electric supercharger, 22 Check valve, 23 Surge tank, 24 Independent intake passage, 25 Intake pressure sensor, 26 Common exhaust passage, 27 flaps, 28 flap actuators 30 exhaust gas purification catalyst, 31 particulate filter, 32 casing, 33 first temperature sensor, 34 second temperature sensor, 35 exhaust opening / closing valve, 41 EGR device, 42 EGR passage, 43 EGR cooler, 44 EGR control valve 46, suction port, 47 discharge port, 48 compressor unit, 49 motor unit, 50 cooling water jacket, 51 engine speed sensor, 52 crank angle sensor, 53 engine water temperature sensor, 54 accelerator opening sensor, 55 intake air temperature sensor, 56 Clutch sensor.

Claims (3)

An exhaust turbocharger,
An intake passage upstream from the compressor of the exhaust turbocharger is connected to an exhaust passage downstream from the turbine of the exhaust turbocharger, and a part of the exhaust gas in the exhaust passage is connected to the intake passage. An EGR passage for reflux;
An EGR valve disposed in the EGR passage for adjusting a recirculation state of exhaust gas;
An intake control valve that is disposed in an intake passage upstream of a connection portion between the EGR passage and the intake passage, and controls the flow rate of air in the intake passage;
An electric supercharger disposed in the intake passage;
Electric supercharger control means for controlling the operation of the electric supercharger;
Fuel increasing means for increasing the amount of fuel injected into the engine when the engine speed drops below a preset reference value when starting the vehicle;
When the engine operating state is in a premixed combustion region set in advance, the intake control valve and the EGR valve are controlled so that the exhaust gas recirculates, and the fuel injection timing is advanced to perform premixed combustion. An engine supercharging device comprising premixed combustion control means for performing
The electric supercharger control means is configured to operate the electric supercharger when the engine speed drops below the reference value when the vehicle starts,
The engine supercharging device, wherein the premixed combustion control means is configured to perform premixed combustion when the engine speed decreases below the reference value when the vehicle starts. Intake valve control means for controlling the opening and closing timing of the intake valve,
The engine supercharging device according to claim 1, wherein the intake valve control means is configured to retard the closing timing of the intake valve when the vehicle starts.   The electric supercharger control means operates the electric supercharger in advance at a speed lower than the normal operation speed when the start of the clutch operation is detected when the vehicle starts, and the engine speed after the clutch operation is started. 2. The engine supercharging device according to claim 1, wherein the electric supercharger is configured to operate at a normal operating rotational speed when the engine pressure drops below the reference value. 3.

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