JP5163540B2 - Diesel engine combustion control system - Google Patents

Description

  The present invention relates to a combustion control device for a diesel engine.

  At the time of transition to premixed combustion, there is one that performs pilot injection to prevent deterioration of combustion noise (see Patent Document 1).

  This will be described. In this example, a premixed combustion region and a diffusion combustion region are determined in advance, and premixed combustion is performed when the operating condition is switched from the diffusion combustion region to the premixed combustion region. In this case, there is a gap between the intake oxygen concentration when the diffusion combustion is performed and the intake oxygen concentration when the premixed combustion is performed, and the actual intake oxygen concentration is just because the operation region is switched. Does not change stepwise, but continuously changes from the intake oxygen concentration at which diffusion combustion is performed to the intake oxygen concentration at which premix combustion is performed. In other words, if premixed combustion is performed during the transition period from the intake oxygen concentration at the time of performing the diffusion combustion to the intake oxygen concentration at the time of performing the premixed combustion, if the intake oxygen concentration is high, the premixing is performed. Qi burns rapidly and combustion noise increases. Therefore, the deterioration of combustion noise is prevented by performing the pilot injection in the above transition period. Specifically, the pilot injection amount is decreased as the intake oxygen concentration decreases during the transition period.

JP 2007-2111768

  By the way, in recent years, various types of premixed combustion have been developed to simultaneously reduce smoke and NOx, and the intake oxygen concentration is diffused when the operating condition is switched from the diffusion combustion region to the premixed combustion region. The inventor investigated the characteristics of combustion noise with respect to the intake oxygen concentration during this transition period, with the period from the decrease in intake oxygen concentration optimal for combustion to the optimum intake oxygen concentration for premixed combustion as the transition period. However, it has been found that there is a combustion noise characteristic that increases and peaks as the intake oxygen concentration decreases and then decreases. In the technique of Patent Document 1, combustion noise cannot be efficiently reduced for the combustion noise characteristic that increases and peaks as the intake oxygen concentration decreases as described above. This is because the technique of Patent Document 1 considers that the combustion noise decreases as the intake oxygen concentration decreases, and the pilot injection amount decreases as the intake oxygen concentration decreases corresponding to such combustion noise characteristics. is there.

  Therefore, the present invention has an object to provide an apparatus capable of efficiently reducing combustion noise even with a combustion noise characteristic that increases and peaks as the intake oxygen concentration decreases during the transition period and then decreases. .

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention comprises an intake oxygen concentration detection / estimation means for detecting or estimating the intake oxygen concentration and an intake oxygen concentration adjustment device (5) capable of adjusting the intake oxygen concentration, and adjusts the intake oxygen concentration in the first operating region. Using the device (5), the first combustion mode which is combustion mainly composed of premixed combustion is performed in a state where the intake oxygen concentration is set to a relatively small first predetermined value, and adjacent to the first operation region. A second firing mode that is different from premixed combustion in a state where the intake oxygen concentration is set to a second predetermined value larger than the first predetermined value using the intake oxygen concentration adjusting device (5) in the second operation region. When the second operation region is switched to the first operation region, the detected or estimated intake oxygen concentration is reduced to a third value between the second predetermined value and the first predetermined value. The intake oxygen concentration is increased until reaching the predetermined value and then the intake oxygen concentration is increased. So it is reduced enough to decrease, to set the fuel injection amount of the pilot injection, is configured to perform pilot injection preceding the main injection using the set pilot injection quantity.

  According to the present invention, the intake oxygen concentration detecting / estimating means for detecting or estimating the intake oxygen concentration and the intake oxygen concentration adjusting device capable of adjusting the intake oxygen concentration are provided, and the intake oxygen concentration adjusting device in the first operation region. Is used to cause the first combustion mode, which is combustion mainly composed of premixed combustion, in a state where the intake oxygen concentration is set to a relatively small first predetermined value, and the second operation adjacent to the first operation region is performed. A second combustion mode that is different from the premixed combustion in a state where the intake oxygen concentration is set to a second predetermined value larger than the first predetermined value using the intake oxygen concentration adjusting device in the region; When switching from the operation region to the first operation region, the detected or estimated intake oxygen concentration decreases until reaching a third predetermined value between the second predetermined value and the first predetermined value. Inspired oxygen concentration decreases as it increases and then The fuel injection amount of the pilot injection is set so that the fuel injection amount is reduced, and the pilot injection prior to the main injection is performed using the set pilot injection amount, so that the intake oxygen concentration is reduced from the second predetermined value and 1 The combustion noise can be efficiently reduced even with the combustion noise characteristic that increases and peaks as the intake oxygen concentration decreases during the transition period until reaching a predetermined value.

It is a schematic block diagram of the combustion control apparatus of the diesel engine of 1st Embodiment of this invention. It is a characteristic view which shows the change of the heat release rate with respect to the crank angle by new premixed combustion. It is sectional drawing which shows the mode in a combustion chamber when main injection is performed just before the compression top dead center. It is a driving | running area figure with respect to an engine speed and an engine load. It is a flowchart for demonstrating combustion control. It is a characteristic view which shows the change of the combustion chamber pressure twice differential value with respect to a crank angle. It is a characteristic view of the fuel amount of the preceding injection of another example. It is a characteristic view of the injection start time of the preceding injection of another example. 6 is a timing chart showing changes in pilot injection amount, EGR rate, and intake oxygen concentration during a transition period from a C region to a B region. FIG. 6 is a characteristic diagram of combustion noise and premixing ratio with respect to intake oxygen concentration during a transition period. It is a flowchart for demonstrating the setting of a transfer flag. It is a flowchart for demonstrating the setting of the pilot injection quantity of a transition period. It is a flowchart for demonstrating switching of the actual combustion form at the time of switching from C area | region to B area | region. It is a characteristic view of an EGR gas flow rate.

  FIG. 1 is a schematic configuration of a diesel engine combustion control apparatus according to an embodiment of the present invention. In FIG. 1, diesel that collects particulate matter (Particulate Matter), which is particulate matter in exhaust gas, for exhaust gas purification in an exhaust passage 40 of a diesel engine (hereinafter simply referred to as “engine”) 1. A particulate filter 16 is provided. The diesel particulate filter 16 traps NOx in the exhaust when the exhaust air-fuel ratio is lean, and a NOx trap catalyst and an oxidation catalyst that can desorb and purify the trapped NOx when the exhaust air-fuel ratio is rich. A (noble metal) may be supported and may have a function of removing exhaust components (NOx, HC, CO) that flow in.

  As an EGR device (exhaust gas recirculation device), an EGR passage 4 and an EGR valve 5 are provided. That is, an EGR passage 4 is provided in the exhaust passage 40 to connect the upstream exhaust outlet passage 40a and the intake collector 20b of the intake passage 20, and the opening of the EGR passage 4 is connected to the intake collector 20b by the stepping motor. A continuously controllable EGR valve 5 is interposed.

  An EGR cooler 17 that cools the exhaust gas flowing through the EGR passage 4 is provided in the middle of the EGR passage 4. The EGR cooler 17 is provided with water amount adjusting means (or water temperature adjusting means such as an electric fan) 44. As the water amount adjusting means, a proportional solenoid type electromagnetic valve or a control valve driven by a step motor or the like can be used. The EGR gas temperature is adjusted by changing the cooling efficiency of the cooler 17 by adjusting the amount of water (or water temperature), and the working gas temperature flowing into the engine 1 is controlled. This working gas temperature is detected by a temperature sensor 41 facing the intake collector 20b. The temperature of the EGR gas introduced into the intake collector 20b is detected by the EGR gas temperature sensor 42.

  An air cleaner 20a is provided upstream of the intake passage 20, and an intake throttle valve 6 that is opened and closed by an actuator (for example, a stepping motor type) is provided between the air cleaner 20a and the intake collector 20b. An air flow meter 7 for detecting the intake air amount Qair, an intake air temperature sensor 8 for detecting the intake air temperature Tair, and an intake air pressure sensor 9 for detecting the intake air pressure Pair are disposed downstream of the air cleaner 20a.

  The engine 1 includes a common rail fuel injection device 10. The common rail type fuel injection device 10 is roughly constituted by a supply pump 11, a common rail (pressure accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder, and fuel pressurized by the supply pump 11 is supplied to a fuel supply passage 12. And once stored in the common rail 14, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valves 15 of each cylinder.

  The common rail 14 is provided with a pressure sensor 34 and a temperature sensor 35 in order to detect the fuel pressure and fuel temperature in the common rail 14. Further, in order to control the fuel pressure in the common rail 14, a part of the fuel discharged from the supply pump 11 is returned from the overflow passage (not shown) to the fuel supply passage via the pressure control valve 13. The pressure control valve 13 can change the flow passage area of the overflow passage in accordance with the duty signal from the engine control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the fuel pressure in the common rail 14 is controlled.

  The fuel injection valve 15 provided facing the combustion chamber is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30. The fuel is injected into the combustion chamber by the ON signal, and the fuel injection is stopped by the OFF signal. The fuel injection amount increases as the ON signal period commanded to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases. According to the common rail fuel injection device 10, it is possible to easily perform the preceding injection and the pilot injection prior to the main injection.

  Each cylinder of the engine 1 is provided with a pressure sensor 2 for detecting the in-cylinder pressure. As the pressure sensor, a type facing the combustion chamber or a washer-shaped knocking sensor type can be used. A water temperature sensor 31 that detects the coolant temperature is attached to the engine 1 at an appropriate position as a representative of the engine temperature.

  The engine control unit 30 includes a signal (CP) from the pressure sensor 2, a signal from the water temperature sensor 31 (cooling water temperature Tw), a signal from the crank angle sensor 32 (a crank angle signal that is the basis of the engine speed Ne), and a crank angle sensor. 33 signal (cylinder discrimination signal Cy1), signal of the pressure sensor 34 for detecting the fuel pressure of the common rail 14 (common rail pressure Pcr), signal of the fuel temperature sensor 35 (fuel temperature Tf), and depression amount of the accelerator pedal corresponding to the load Accelerator opening sensor 50 signal (accelerator opening (load) Acc), air flow meter 7 signal (intake air amount Qair), intake air temperature sensor 8 signal (intake air temperature Tair), intake air pressure sensor 9 signal (Intake pressure Pair) and a signal (Tgas) of the working gas temperature sensor 41 are respectively input. .

Further, an oxygen concentration (air-fuel ratio) sensor 43 for detecting the exhaust oxygen concentration (O ₂ exh) is provided at the outlet portion (or the inlet portion) of the diesel particulate filter 16 in the exhaust passage 40, and this signal is also sent to the engine control unit. 30. As the exhaust oxygen concentration sensor 43, for example, a sensor that detects the exhaust oxygen concentration using an oxygen ion conductive solid electrolyte can be used.

  In the engine control unit 30, based on these input signals, an opening command signal for the overflow passage to the pressure control valve 13 for controlling the injection amount and timing of fuel injection and a fuel injection command signal to the fuel injection valve 15. , An opening command signal to the intake throttle valve 6, an opening command signal to the EGR valve 5, a water amount adjustment signal to the water amount adjusting means 45, and the like are output.

  Now, combustion based on premixed combustion (hereinafter referred to as “premixed combustion”) (first combustion mode), which is a premise of the present invention, will be described first. This premixed combustion is good for lowering the NOx, because the lower the intake oxygen concentration is, the lower the combustion temperature is. However, the stability of ignition is lowered, the unburned HC due to poor ignition increases, and the ignition is too early. It was newly devised to solve the problem of combustion becoming diffusive and increasing smoke. In this new premixed combustion mode, an air-fuel mixture that is leaner than stoichiometric (stoichiometric air-fuel ratio) (hereinafter simply referred to as “lean air-fuel mixture”) and richer than stoichiometric in the combustion chamber before ignition is performed prior to main injection. This is characterized in that combustion is started in a situation where the lean mixture (hereinafter simply referred to as “rich mixture”) is unevenly distributed and the lean mixture and rich mixture are unevenly distributed.

  To briefly describe the premix combustion of the conventional device, fuel injection is executed early in the compression process to reduce smoke, and a uniform premixed gas is formed to ignite and burn near the compression top dead center. Uniform premixed combustion, so-called HCCI, has been proposed. In this combustion method, fuel injection is performed outside the piston cavity when the pressure inside the cylinder is low and the fuel spray penetration is relatively strong, and the piston is descending. It will stick. For this reason, problems such as dilution of lubricating oil with fuel, increase in CO emissions due to unburned fuel (HC) and incomplete combustion occur. In addition, the ignition / combustion timing of the premixed gas becomes unstable, and sudden combustion occurs at the time of ignition, resulting in a problem that combustion noise increases.

  In addition, a small amount of fuel is pilot-injected near the top dead center before the main injection, premixed and combusted after the top dead center, and in the expansion stroke after the combustion of the pilot-injected fuel, the original pressure and temperature are reduced and only the main injection is performed. Has proposed a combustion method in which main injection fuel is injected at a time when combustion is not stable and misfire occurs (see Japanese Patent No. 3613666). In this combustion method, since the main injection is executed after the compression top dead center after the combustion of the pilot fuel, the temperature in the combustion chamber rises due to the combustion of the pilot fuel, but the intake oxygen concentration is lowered and the ignitability is easily offset. . In addition, the main injection fuel is injected at a time when the pressure and temperature drop and the main injection alone does not stabilize the combustion, and misfires occur. If the timing fluctuates and retards, or if the intake air temperature decreases, there is a problem that it is easy to misfire and combustion control becomes difficult.

  On the other hand, in order to increase combustion efficiency and optimize the premixed combustion speed to prevent an increase in vibration noise due to rapid combustion, early injection that is executed once or a plurality of times at the early stage of the compression process, and early injection end There has been proposed a combustion method in which fuel injection is performed by dividing into later main injection near the compression top dead center, and heat generation by main injection is generated after heat generation by early injection is completed (Japanese Patent Application Laid-Open (JP-A)). 2004-218612, JP-A-2003-286879, JP-A-2004-176593).

  However, when performing early injection, early injection is performed in a state where the temperature in the cylinder is low and the temperature is low so that the injected fuel does not ignite immediately. Unless the distribution of equivalence ratio (air mixture concentration) in the combustion chamber is appropriate and the ignition timing or ignition area of each injected fuel is appropriate, vibration noise caused by rapid combustion by optimizing the combustion speed while maintaining high thermal efficiency It was found that the increase in the amount could not be prevented.

  Although the fuel injected early is likely to premix combustion prior to the main injection, in order to increase the thermal efficiency, it is desirable to start the heat generation by the early injection and the main injection from the compression top dead center. If combustion due to early injection occurs early before compression top dead center (when the oxygen concentration of the intake gas is relatively high or the gas temperature is high), due to an increase in the temperature in the combustion chamber due to combustion of the early injection fuel, or When the main injection fuel enters the combustion flame of the early injection fuel, ignition combustion of the main injection fuel is promoted. For this reason, not only the thermal efficiency is lowered, but also the diffusion burnup of the main injection fuel is increased and smoke is increased.

  Conversely, when combustion by early injection and main injection occurs after compression top dead center, if the intake gas temperature and oxygen concentration are relatively low, the prediction from the end of main injection to the start of combustion of main injection fuel is possible. There is a problem that the combustion period can hardly be reduced because the mixing period becomes longer and the leanness of the main injection fuel progresses, and the equivalence ratio distribution almost disappears at the time of ignition, resulting in sharp combustion with a high premixing ratio. . Or, when the leaning progresses transiently, the ignition and combustion timing of the main injected fuel becomes unstable, which causes problems such as the discharge of unburned fuel (HC) due to misfire and CO deterioration due to incomplete combustion. I found it to happen.

  Therefore, in order to keep the thermal efficiency at the ignition timing high and optimize the combustion speed to prevent the increase of vibration noise due to rapid combustion, and to reduce the generation of unburned components such as HC and CO and smoke, early injection fuel Control the premixing period or ignition timing of the main injection fuel to prevent the early injection fuel from burning before the main injection, and the premixing period from the end of the main injection to the start of combustion of the main injection fuel will be prolonged. It is necessary to prevent the leaning of the injected fuel from proceeding excessively, that is, it is necessary to optimize the equivalence ratio (air mixture concentration) distribution in the combustion chamber at the ignition timing.

  Therefore, the present inventor conducted an experiment by advancing the fuel injection prior to the main injection to a range that is not conceivable in the conventional apparatus, and the injection timing of the main injection is set to the advance side with respect to the compression top dead center TDC. As a result of performing a combustion analysis using the heat release rate (HRR) and the combustion mass ratio (Mass Burnt), it has been found that a satisfactory new premixed combustion is found.

  Note that fuel injection that is performed at an advanced timing that cannot be considered in the above-mentioned “early injection” is defined as “preceding injection”. That is, “preceding injection” and the above “early injection” are the same in that they are fuel injection prior to main injection, but the injection timing is an advanced timing that cannot be considered in “early injection”. As described later, and as will be described later, it is also different from “early injection” in that the ratio of the preceding injection amount to the main injection amount is several times larger than the ratio of the early injection amount to the main injection amount.

  This new premixed combustion will be described with reference to FIG. The preceding injection prior to the main injection (indicated as “1st Inj” in the figure) not only forms a pre-combustion mixture, but also forms a lean mixture that contributes to reducing combustion noise during main injection combustion. Therefore, more fuel (for example, 20 to 40%) is injected than the injection amount (for example, about 10%) of the early injection for the purpose of preliminary combustion in the conventional apparatus.

  In order to prevent most of the air-fuel mixture near the compression top dead center TDC by the pre-injected fuel from becoming an easily burnable equivalence ratio, that is, to make only a part of the air-fuel mixture causing pre-combustion an easily burnable equivalent ratio, Pre-injection is performed at a timing (for example, before BTDC 30 °) considerably earlier than an injection timing (for example, a timing later than BTDC 30 °) of the early injection for the purpose of preliminary combustion.

  On the other hand, if the pre-injection is performed too early, the air-fuel mixture formed by the pre-injection near the compression top dead center TDC is diffused too much in the entire combustion chamber (because it is too diluted), or combustion does not occur. The time from the injection timing to the compression top dead center TDC is long, the pressure in the combustion chamber at the time of the preceding injection is low, the fuel spray penetration becomes strong, the fuel spray adheres to the bore wall, Since unburned HC increases, there is a limit even if it is made early. Therefore, the injection timing of the preceding injection is considered after the compression top dead center (BTDC) 60 ° after this limit. Therefore, as shown in FIG. 2, the injection timing of the preceding injection is set to 60 ° before compression top dead center (BTDC) and 30 ° before compression top dead center (BTDC).

  In this way, the pre-injection amount is several times larger than the early injection amount for the purpose of preliminary combustion in the conventional device, but this large amount of pre-injection fuel is used as the main injection (indicated as “Main Inj.” In the figure). In order not to burn until the time when spraying is late (the time when compression top dead center TDC is passed), the oxygen concentration at the time of early injection for the purpose of preliminary combustion in conventional devices (for example, about 17 to 18%) is significantly lower The oxygen concentration (for example, 12 to 15%) (first predetermined value) is set.

  In order to premix, the main injection is also finished before the compression top dead center TDC. In particular, it has been found that if heat is generated near the compression top dead center TDC (the pre-combustion peak starts near the compression top dead center TDC), combustion noise is reduced and smoke is improved. In order to generate heat from the vicinity of the compression top dead center TDC, the main injection is finished in the vicinity of the compression top dead center TDC (the optimal injection timing of the preceding injection also changes). That is, as shown in FIG. 2, the injection end timing of the main injection is set immediately before the compression top dead center TDC. FIG. 3 shows a state in the combustion chamber when main injection is performed immediately before the compression top dead center TDC.

  Next, the action of the new premixed combustion will be described.

  A lean mixture with a relatively flammable equivalent ratio, which is relatively delayed in the pre-injected lean mixture, and a part of the main injected fuel, which has a relatively advanced diffusion / premix An air-fuel mixture with an equivalent ratio of flammability causes a low-temperature oxidation reaction in the vicinity of TDC to form a preliminary combustion.

  As a result, when the temperature and pressure in the combustion chamber rise, a high temperature oxidation reaction of the rich mixture by the main injection fuel starts. By the time the pre-combustion ends, the main injection fuel is also diffused and pre-mixed in the combustion chamber, so it becomes a rich mixture with an equivalence ratio that is relatively easy to burn and begins to produce a high-temperature oxidation reaction (diffusive combustion). .

  The high-temperature oxidation reaction (diffusion combustion) of the rich mixture by the main injection fuel also causes the combustion of the remaining lean mixture (premixed combustion) that did not burn in the pre-combustion. Combustion of air and lean mixture, that is, diffusive combustion and premixed combustion are mixed.

  The main injection fuel constituting the main combustion is a rich mixture and mainly consists of diffusive combustion. However, since the diffusion and premixing are relatively advanced, smoke can be suppressed. In addition, since it is mainly diffusive combustion, the steepness of combustion, that is, combustion noise is also reduced.

  On the other hand, the lean mixture by the pre-injection, which is another mixture that constitutes the main combustion, is moderately combusted, and these coexistence reduces the combustion noise and the combustion temperature as a whole. Furthermore, NOx is reduced.

  Further, the combustion of the lean mixture is promoted along with the combustion of the rich mixture, and there is no problem of unburned HC emission due to the unburned lean mixture.

  In other words, a lean mixture with a relatively flammable equivalent ratio, which is relatively delayed in the lean mixture by the pre-injected fuel, and a relatively advanced diffusion / premix in the main injected fuel. Some of the flammable mixture with an equivalent ratio causes a low temperature oxidation reaction near the compression top dead center TDC to cause pre-combustion, and then the rich mixture by the main injection with advanced diffusion and premixing in the combustion chamber. The main combustion is performed with the lean air-fuel mixture obtained by the preceding injection that is not used for the preliminary combustion.

  According to such new premixed combustion, the following effects can be obtained.

  In the new combustion mode, when the intake oxygen concentration is greatly reduced to reduce NOx, ignition is performed after the equivalence ratio is distributed in light and shade with the stoichiometric ratio (combustion starts). Can reliably ignite, and unburned HC due to poor ignition can be reduced.

  On the other hand, the pre-injection for distributing the lean air-fuel mixture is performed early (much early), so that the air-fuel mixture by the pre-injection is prevented from having an equivalent ratio that is easy to burn before compression top dead center. It is possible to suppress ignition and ignition at the early injection period and to suppress the diffusive combustion of the main injection fuel.

  Since the intake oxygen concentration is greatly reduced, the precipitous combustion of the rich mixture that undergoes premix combustion can be mitigated, and the rich mixture and lean mixture coexist. Even if the combustion is steep, the slow combustion of the lean air-fuel mixture can suppress the steepness of the combustion as a whole and reduce the combustion noise.

  On the other hand, the combustion of the lean mixture tends to be incomplete, but the relatively sharp combustion of the rich mixture cancels out (to promote the combustion of the lean mixture) and the combustion becomes incomplete. Can be prevented.

  Now, the new premixed combustion cannot be realized in all the operation regions, and is limited to a part of the operation regions as shown in FIG. That is, the engine speed Ne and the engine load (for example, accelerator opening degree Acc) are used as parameters, and the operation area is largely divided into four areas of A area, B area, C area, and D area from the low load side, and the lowest Side A area is a normal combustion permission area, B area is an EGR permission area and premixed combustion permission area, C area is an EGR permission area and normal combustion permission area, D area is an EGR non-permission area and normal combustion permission area Determine as Here, “normal combustion” refers to conventional diesel combustion, that is, combustion mainly consisting of diffusion combustion (hereinafter referred to as “diffusion combustion”) (second combustion mode). This is the new premixed combustion explained in. Thus, new premixed combustion is performed only in the B region. In the B region, the intake oxygen concentration can be controlled by EGR control, so that the intake oxygen concentration in the B region is controlled to be the first predetermined value a by EGR control.

  The engine load [%] on the vertical axis shown in FIG. 4 may be selected as follows. That is, the accelerator opening Acc [deg] and the throttle opening TVO [deg] correspond to 1: 1 (the accelerator opening when the accelerator pedal is not depressed is the throttle opening when idling, the accelerator pedal The accelerator opening when fully depressing the position corresponds to the throttle opening when fully open), so if you change the value obtained by dividing the current accelerator opening Acc [deg] by the maximum accelerator opening [deg] to% display The engine load [%] on the vertical axis can be obtained. In order to obtain the engine speed [%] on the horizontal axis, a value obtained by dividing the current engine speed Ne [rpm] by the maximum speed [rpm] may be changed to% display. Note that an operating region diagram in which the horizontal axis indicates the engine speed Ne [rpm] and the vertical axis indicates the accelerator opening degree Acc [deg] may be used.

  The combustion control of the present invention performed by the engine control unit 30 will be described with reference to the flowchart of FIG.

In step 1, in-cylinder pressure CP, intake air amount Qair, intake air temperature Tair, intake air pressure Pair, water temperature Tw, engine speed Ne, cylinder discrimination signal Cyl, common rail pressure Pcr, fuel temperature Tf, accelerator opening Acc, Signals corresponding to the intake gas temperature Tgas, the EGR gas temperature Tegr, and the exhaust oxygen concentration O ₂ exh are read.

  In step 2, the current rotational speed and load, and the engine temperature state are detected from the engine rotational speed Ne, the accelerator opening Acc, the water temperature Tw, and the like.

  In step 3, a target value for fuel injection by the common rail is calculated, and drive control of the fuel injection valve 15 is executed. For this reason, the pressure control is first performed. The common rail pressure control is performed by searching a predetermined map stored in advance in the ROM of the engine control unit 30 using the engine speed Ne and the load Acc as parameters. A target reference pressure PCR0 is obtained, and feedback control of the pressure control valve 13 is executed so that the target reference pressure PCR0 is obtained.

  The fuel injection timing is controlled. For example, with the engine speed Ne and the load Acc as parameters, the fuel injection amount Qpilot for pilot injection, the fuel injection amount Q main for main injection, the common rail pressure (injection pressure) PCR, the injection period P period for pilot injection, and the injection period for main injection M period, injection start timing MIT of main injection, injection start timing PIT of pilot injection, etc. are obtained by searching predetermined map data stored in the ROM of the engine control unit 30 in advance. Then, based on the crank angle signal of the crank angle sensor 32 and the cylinder discrimination signal Cyl of the crank angle sensor 33, the pilot injection fuel injection amount Qpilot and the main injection fuel injection amount Qmain are supplied. The fuel injection valve 15 of the cylinder to be injected is driven to open during the injection period P period of the pilot injection from the injection start time PIT and during the injection period M period of the main injection from the injection start time MIT of the main injection.

  Here, the fuel injection amount Qpilot of the pilot injection includes the injection amount of the preceding injection performed in the B region, and the injection period P period of the pilot injection includes the injection period of the preceding injection performed in the B region. This injection start timing PIT includes the injection start timing of the preceding injection performed in the B region. This is defined as fuel injection in which pilot injection is performed in at least the C region of the A region, the C region, and the D region, and the preceding injection is performed in the B region, but the pilot injection is performed prior to the main injection. For example, since the preceding injection is also a pilot injection, the preceding injection is included as a pilot injection. In terms of control, the pilot injection control amount (injection amount, injection period, injection start timing) retrieved in the B region from the map is treated as the control amount (injection amount, injection period, injection start timing) of the preceding injection. Become.

  In step 4, as shown in FIG. 4, the operating conditions determined from the engine speed Ne and the accelerator opening Acc as the engine load are a predetermined normal combustion permission region (A region), EGR permission region, and It is determined whether the premixed combustion permission area (B area), the EGR permission area and the normal combustion permission area (C area), or the EGR non-permission area and the normal combustion permission area (D area).

  As a result of this determination, the routine proceeds to step 5 only when the operating condition is in the EGR permission region and the premix combustion permission region (B region), and the main injection premix control period (MPI: end of main injection and start of combustion of main injection) ). As shown in FIG. 2, in the new premixed combustion, after most of the fuel to be injected is injected, the heat generation of the pre-injection and the low-temperature oxidation reaction of the main injection occur at the same time. Oxidation reaction). That is, ignition / combustion is started in a state where the lean air-fuel mixture formed by the preceding injection and the relatively rich air-fuel mixture formed by the main injection are mixed in two. In other words, if the detected value in the premix control period matches the target value in the premix control period, new premix combustion can be realized.

Here, as a method for determining the combustion start timing of the main injection, as shown in FIG. 6, the combustion chamber pressure twice differential value dP ₂ / dθ ₂ [kPa / deg ² ] of the in-cylinder pressure CP can be used. . For example, as shown in FIG. 6, a point at which the differential value twice in the combustion chamber pressure once becomes a negative value and then rises again and crosses the zero point is defined as the combustion start timing of the main injection. In this way, the combustion start timing of the main injection can be detected.

The parameter for detecting the combustion start timing of the main injection is not limited to the combustion chamber pressure twice differential value dP ₂ / dθ ₂ . For example, instead of the combustion chamber pressure twice differential value dP ₂ / dθ ₂ , the rise start timing dQ / dθ [J / deg] of the main combustion heat generation rate of the main injection shown in FIG. 2 may be used. In this case, it is desirable to detect the slice level by setting the cross point of the slice level as the combustion start timing of the main injection.

  On the other hand, the injection end timing of the main injection is a timing at which the main injection period M period has elapsed from the main injection start timing MIT, and can be obtained from the main injection start timing MIT and the main injection period M period.

  Here, the fuel amount of the pre-injection and the injection start timing of the pre-injection may simply be a constant value, but the fuel amount of the pre-injection is increased in order to increase the formation of the lean mixture by the pre-injection and increase the combustion noise reduction effect. As shown in FIG. 7, it is desirable to increase the load as the load increases, and as shown in FIG. 8, it is desirable to advance the injection start timing of the preceding injection as the load increases. In addition, unlike the HCCI combustion, the pre-injection is not performed at an early stage where the fuel spray directly collides with and adheres to the inner wall of the cylinder, and unlike the pilot injection based on the conventional diffusion combustion. It is not injected close to the main injection. The injection start timing of the preceding injection is preferably performed at the timing at which most of the preceding injected fuel is injected into the piston cavity, but in order to more reliably prevent the collision of fuel spray with the cylinder inner wall, the number of injections of the preceding injection It is also effective to decrease the penetration by increasing the load as the load increases.

  In step 6, a target value for the premix control period is calculated. In other words, at the ignition timing of the main injection fuel, the mixture of the pre-injection fuel that has been appropriately leaned in the combustion chamber and the mixture of the main injection fuel that has not been too lean are mixed in two in advance. The target value of the premix control period obtained by experiment etc. is retrieved from the map data stored in advance in the ROM of the engine control unit 30 using the engine speed Ne and the accelerator opening Acc as the engine load as parameters. And ask.

  If the detected premix control period does not coincide with the premix control period target value, new premix combustion cannot be realized. Therefore, in step 7, the detected premix control period and the calculated premix control period target are set. A new premixed combustion is realized by controlling the ignition timing based on the deviation from the value (dMPI). Specifically, when the premix control period detection value is longer than the premix control period target value, the ignition timing is advanced and the premix control period is adjusted to the target value. Conversely, when the premix control period detection value is shorter than the premix control period target value, the ignition timing is delayed to match the premix control period to the target value.

  Means for variably controlling the ignition timing include a method of controlling the fuel injection timing and pressure, a method of variably controlling the temperature and pressure of the intake gas, the compression ratio, etc., and controlling the compression end temperature, the intake oxygen concentration, There is a method of variably controlling the residual gas ratio, and it is possible to arbitrarily control the ignition timing by adopting any of these methods.

  This completes the description of the new premixed combustion that is the premise of the present invention.

  Now, when the operating condition in FIG. 4 is switched from the C region (EGR permission region and normal combustion permission region) to the B region (EGR permission region and premixed combustion permission region), the combustion noise deteriorates. It has been found. An analysis of this will be described with reference to FIGS.

  The upper, middle, and lower stages in FIG. 9 show how the pilot injection amount, EGR rate, and intake oxygen concentration change when switching from the C region to the B region. Further, the combustion mode and the operation region are shown in the upper part of the upper stage.

  Since the operating condition is switched from the C region to the B region at the timing t1, the intake oxygen concentration at the timing t1 is changed from the second predetermined value b, which is an optimum value for diffusion combustion in the C region, to B. It is necessary to decrease stepwise to the first predetermined value a which is an optimum value for new premixed combustion in the region. Here, in the B region, the intake oxygen concentration can be adjusted by the EGR valve 5 (EGR device), so that the first predetermined value a which is the optimum intake oxygen concentration for the new premixed combustion in the B region is obtained. , The target EGR rate e in the B region is predetermined. Therefore, at the timing t1 when the operating condition is switched from the C region to the B region, the target EGR rate is changed from the target EGR rate f in the C region to the target EGR rate in the B region, as shown by a one-dot chain line in FIG. Step by step to e.

  However, even if the EGR valve actuator (stepping motor) is instructed to close the EGR valve 5 until the target EGR rate e is obtained from the engine control unit 30, it responds until the EGR valve 5 is actually closed after receiving the command. There is a delay. Even if the EGR valve 5 is closed without a response delay, the actual EGR rate changes with a delay as shown by the solid line in FIG. 9 because there is a volume of piping from the EGR valve 5 to the combustion chamber. At this timing, the actual EGR rate reaches the target EGR rate e. Since the intake oxygen concentration changes according to the actual EGR rate, as shown by the solid line in FIG. 9, it continuously decreases corresponding to the change in the actual EGR rate, and reaches the first predetermined value a at the timing of t3. To reach. That is, the intake oxygen concentration cannot change stepwise from the second predetermined value b to the first predetermined value a at the timing t1, due to the influence of the responsiveness of the EGR valve 5, the volume of the pipe, and the like. It gradually decreases toward a, and finally reaches the first predetermined value a at the timing t3.

  FIG. 10 shows the results of experiments and summary of how the combustion noise and the premixing ratio change with respect to the intake oxygen concentration from the second predetermined value b to the first predetermined value a. Here, the premixing ratio is obtained by dividing the amount of fuel injected into the combustion chamber by the ignition timing of the main injection fuel by the total fuel amount that is the sum of the fuel amount of the preceding injection and the fuel amount of the main injection. It is a value converted to a percentage. This premixing ratio increases as the intake oxygen concentration decreases.

  On the other hand, the combustion noise increases as the intake oxygen concentration decreases from the second predetermined value b, and peaks when the intake oxygen concentration reaches the third predetermined value c, and then suddenly increases as the intake oxygen concentration decreases toward the first predetermined value a. It is getting smaller. When the third predetermined value c is shifted to FIG. 9, the intake oxygen concentration reaches the third predetermined value c at the timing t2. Then, in FIG. 9, the combustion noise gradually increases from the timing of t1 when switching to the B region and takes a peak at the timing of t2, the combustion noise decreases from the timing of t2, and the intake oxygen concentration becomes the first predetermined concentration. It is analyzed that the combustion noise becomes a negligible level at the timing t3 when the value a is reached. That is, as shown in FIG. 10, the intake oxygen concentration increases in the range from the second predetermined value b to the third predetermined value c, and increases as the intake oxygen concentration decreases after the third predetermined value c. In order to prevent combustion noise having a characteristic that becomes smaller this time, as shown by a solid line in FIG. 9, the pilot injection amount given at the timing of switching to the B region is set as an initial value, and the second predetermined value b to the third predetermined value are set. As the intake oxygen concentration decreases to c, the pilot injection amount is increased from the initial value, and as the intake oxygen concentration decreases from the third predetermined value c to the first predetermined value a, this time the pilot at the third predetermined value c. The pilot injection amount is decreased from the initial value with the injection amount as an initial value, and is made zero at the timing t3 when the intake oxygen concentration reaches the first predetermined value a.

  With the pilot injection amount given at the switching timing to the B region as an initial value, the pilot injection amount is increased from the initial value as the intake oxygen concentration decreases in the range from the second predetermined value b to the third predetermined value c. This is because the combustion noise increases as the intake oxygen concentration decreases toward the third predetermined value c. Further, as the intake oxygen concentration decreases in the range from the third predetermined value c to the first predetermined value a, the pilot injection amount at the third predetermined value c is set to the initial value and the pilot injection amount is reduced from this initial value. This is because the combustion noise decreases as the intake oxygen concentration decreases toward the first predetermined value a. The role of pilot injection here is to play a role as a seed fire. In other words, combustion noise is generated when the premixed gas in the diffusion combustion is rapidly burned. Therefore, a pre-mixture is created before the premixed gas in the diffusion combustion is burnt rapidly, and thereby, the premixed gas in the diffusion combustion is created. This prevents the combustion from abruptly and prevents combustion noise. As described above, according to the present invention, the transition is performed by performing the pilot injection in the transition period in which the intake oxygen concentration decreases from the second predetermined value b to the first predetermined value in accordance with the characteristics of the combustion noise shown in FIG. Combustion noise could be prevented throughout the period.

  On the other hand, the actual EGR rate increases during the transition period until the intake oxygen concentration reaches the optimum intake oxygen concentration for premix combustion in order to prevent deterioration of combustion noise when switching to the premix combustion region There is a conventional device that reduces the pilot injection amount as the number of pilot injections increases. However, if this conventional apparatus is applied as it is during the transition period which is the subject of the present invention, deterioration of combustion noise cannot be effectively prevented. That is, if the conventional apparatus is applied as it is during the transition period that is the subject of the present invention, the characteristics of the pilot injection amount are as shown by the one-dot chain line in FIG. 9, and the pilot injection amount decreases as the actual EGR rate increases. Become. However, according to the characteristics of the combustion noise shown in FIG. 10, the combustion noise increases while the intake oxygen concentration in FIG. 9 decreases from the second predetermined value b to the third predetermined value c. However, the pilot injection amount must be increased as in the present invention. However, in the conventional apparatus, on the contrary, the pilot injection amount is decreased, so that combustion noise cannot be effectively suppressed.

  Further, in the present invention, instead of switching to the new premixed combustion at the timing t1 when the operating condition is switched to the B region, the diffusion combustion in the C region is continued as it is after the timing t1, and the intake oxygen concentration becomes the first. 1 At t3 when the predetermined value a is reached, the diffusion combustion in the C region is switched to the new premixed combustion (see FIG. 9).

  Next, details of the control executed by the engine control unit 30 will be described with reference to the flowcharts of FIGS.

  First, FIG. 11 is for setting a transition flag, which is executed at regular time intervals (for example, every 10 msec).

  In step 11, the accelerator opening Acc as the engine load and the engine speed Ne are read. In step 12, the operating conditions determined from the engine load and the engine speed are switched from the C region to the B region shown in FIG. See if it was. If the operating condition is not at the timing when the C region is switched to the B region, the current process is terminated.

  On the other hand, when the operating condition is switched from the C region to the B region, the process proceeds from step 12 to step 13 to set the transition flag (initially set to zero when the engine is started) = 1. The target EGR rate increases stepwise from the target EGR rate f in the C region to the target EGR rate e in the B region in an EGR control routine (not shown) at the timing when the operating condition is switched from the C region to the B region. (See the dashed line in FIG. 9).

  FIG. 12 is for setting the pilot injection amount in a transition period, which is a period until the intake oxygen concentration decreases from the second predetermined value b and settles to the first predetermined value a. (For example, every 10 msec).

  In step 21, the transition flag (set according to FIG. 11) is observed. If the transition flag = 0, the current process is terminated.

On the other hand, when the transition flag = 1, it is determined that it is in the transition period, the process proceeds from step 21 to step 22, and the intake oxygen concentration O ₂ int detected by the intake oxygen concentration sensor is read. Here, in order to detect the intake oxygen concentration O ₂ int, an intake oxygen concentration sensor is provided in the intake collector 20b.

In step 23, the intake oxygen concentration O ₂ int is compared with a third predetermined value c. The third predetermined value c is the intake oxygen concentration when the combustion noise peaks during the transition period. The third predetermined value c is determined in advance by adaptation. When the intake oxygen concentration O ₂ int is larger than the third predetermined value c, the routine proceeds to step 24, where the pilot injection amount in the C region immediately before the transition flag = 1 is set as the initial value and the pilot injection amount is increased. For example, if the pilot injection amount in the C region is PiQ0, the first time (shift start timing) when switching to the B region is obtained by multiplying this by the increase coefficient α as a pilot injection amount, that is, PiQ = α × PiQ0 (( 1)
The pilot injection amount PiQ at the transition start timing is calculated by the following formula, and thereafter
PiQ = α × PiQ (previous) (2)
However, PiQ (previous): previous value of PiQ,
The pilot injection amount PiQ is updated to the increase side by the following formula. The increase coefficient α in the above formulas (1) and (2) is a value larger than 1 and is adapted beforehand.

When the intake oxygen concentration O ₂ int is larger than the third predetermined value c, the step 24 is repeated, that is, the equation (2) is repeated using the increase coefficient α, so that the pilot injection amount PiQ increases.

Eventually, when the intake oxygen concentration O ₂ int becomes equal to or smaller than the third predetermined value c in step 23, the process proceeds to step 25, and the intake oxygen concentration O ₂ int and the first predetermined value a are compared. The first predetermined value a is the optimum intake oxygen concentration for combustion in the B region. That is, as described above, the first predetermined value “a” is determined in advance by the intake oxygen concentration that does not cause the low-temperature oxidation reaction until the main injection is completed. When the intake oxygen concentration O ₂ int is larger than the first predetermined value a, the routine proceeds to step 26, where the pilot injection amount at the timing immediately before the intake oxygen concentration becomes equal to or lower than the third predetermined value c is set as the initial value and the pilot injection amount is decreased. . For example, a value obtained by multiplying the previous pilot injection amount by the reduction coefficient β is used as the pilot injection amount, that is, PiQ = β × PiQ (previous) (3)
However, PiQ (previous): previous value of PiQ,
The pilot injection amount PiQ is updated to the decreasing side by the following formula. The weight loss coefficient β in the above equation (3) is preliminarily adapted to a positive value smaller than 1.

When the intake oxygen concentration O ₂ int is larger than the second predetermined value b, the step 26 is repeated, that is, the equation (3) is repeated using the reduction coefficient β, so that the pilot injection amount PiQ is decreased.

Eventually, when the intake oxygen concentration O ₂ int becomes equal to or less than the second predetermined value b in step 25, it is determined that the transition period has ended, that is, it is not necessary to perform further pilot injection. PiQ = 0 and the transition flag = 0. In step 29, the combustion mode switching flag (initially set to zero when the engine is started) is set to 1.

  In the embodiment, it is determined whether to increase or decrease the pilot injection depending on whether the intake oxygen concentration is larger or smaller than the third predetermined value c, but is not limited thereto. For example, since the intake oxygen concentration and the actual EGR rate correspond to 1: 1, as shown in FIG. 9, the actual EGR rate g corresponding to the third predetermined value c can be obtained. If the actual EGR rate g corresponding to the third predetermined value c is the third predetermined value g, the actual EGR rate is compared with the third predetermined value g, and the actual EGR rate is smaller than the third predetermined value g. Then, the pilot injection amount is increased, and if the actual EGR rate becomes equal to or greater than the third predetermined value g, the pilot injection amount may be decreased. Further, when the actual EGR rate reaches the target EGR rate e in the B region, it is determined that the transition period has ended.

  Here, as the actual EGR rate, a load average value of the target EGR rate is used or estimated as follows. That is, the EGR gas flow rate flowing through the EGR valve 5 is calculated by searching a map having the contents shown in FIG. 14 from the opening degree of the EGR valve 5 and the differential pressure across the EGR valve 5, and the EGR gas flow rate and the air flow meter are calculated. 7 is calculated as the actual EGR rate.

  FIG. 13 is for continuing the diffusive combustion in the C region after switching to the B region and switching to a new premixed combustion at the timing when the transition period is completed. Every). Note that FIG. 13 is executed after the operating condition is switched from the C region to the B region.

  In step 31, whether or not the operating condition determined from the accelerator opening as the engine load and the engine speed is in the B region, and in step 32, whether or not the combustion mode switching flag (set according to FIG. 12) = 1. See. If the operating condition is not in the B region, the current process is terminated.

  Even if the operation condition is in the B region, if the combustion mode switching flag = 0, it is determined that the transition period has not yet ended, and the routine proceeds to step 33, where diffusion combustion in the C region is executed. If the operating condition is in the B region and the combustion mode switching flag = 1, it is determined that the transition period has ended, and the routine proceeds to step 34 where new premixed combustion is executed. That is, instead of executing the new premixed combustion immediately after the operating condition is switched to the B region, the diffusion combustion in the C region is continued during the transition period, and the new premixed combustion is performed after the transition period ends. Run.

  Then, the pilot injection prior to the main injection is performed using the pilot injection amount PiQ in the transition period set in FIG. 12 while performing the diffusion mode in the C region until the transition period ends. In FIG. 9, diffusion combustion in the C region is performed until the timing of t1, but pilot injection for realizing this diffusion combustion is performed according to FIG. 5, and from the timing of t1 to immediately before the timing of t3, The pilot injection is performed by replacing the pilot injection amount PiQ in the transition period set in FIG. 12 while maintaining the injection timing of the pilot injection.

  Here, the effect of this embodiment is demonstrated.

  According to the present embodiment (invention described in claim 1), an intake oxygen concentration sensor (intake oxygen concentration detection means) and an EGR valve 5 (intake oxygen concentration adjustment device) are provided, and a region B (first operation) is provided. Region), the premixed combustion (first combustion mode) is performed in a state where the intake oxygen concentration is set to a relatively small first predetermined value a using the EGR valve 5 (see steps 1 to 3 in FIG. 5). In the region C adjacent to the region B (second operating region), the EGR valve 5 is used to perform diffusion combustion (second combustion) with the intake oxygen concentration being set to a second predetermined value b larger than the first predetermined value a. (See Steps 1 to 3 in FIG. 5), and when the C region is switched to the B region, the detected oxygen concentration decreases, and the second predetermined value b and the first predetermined value a Until the third predetermined value c is reached, and after that, the intake oxygen concentration decreases. The fuel injection amount of the pilot injection is set so that the amount is reduced as it goes (see steps 21 to 28 in FIG. 12), and the pilot injection is performed using the set pilot injection amount (steps 31 and 32 in FIG. 13). , 33), the intake oxygen concentration decreases as the intake oxygen concentration decreases during the transition period from the second predetermined value b to the first predetermined value a, and takes a peak and then decreases. Even if it is a combustion noise characteristic, a combustion noise can be reduced efficiently.

  According to the present embodiment (the invention described in claim 2), diffusion combustion (second combustion mode) is performed during the transition period until the intake oxygen concentration decreases from the second predetermined value b and reaches the first predetermined value a. ) Is continued, and when the intake oxygen concentration reaches the first predetermined value a, the pre-mixed combustion (first combustion mode) is switched (see steps 31, 32, 33, steps 31, 32, 34 in FIG. 13). ), Deterioration of combustion noise can be suppressed as compared with the case of switching to premixed combustion (first combustion mode) at the timing of switching from the C region (second operating region) to the B region (first operating region).

 According to this embodiment (the invention described in claim 3), the intake oxygen concentration adjusting device is the EGR valve 5 capable of adjusting the EGR rate, and the intake oxygen concentration estimating means is configured to determine the intake oxygen concentration based on the actual EGR rate. Therefore, the intake oxygen concentration can be estimated without directly detecting the intake oxygen concentration.

 According to the present embodiment (the invention described in claim 4), the first predetermined value a is an intake oxygen concentration that does not cause a low-temperature oxidation reaction until the main injection is completed, and the main injection is performed during the compression process. After performing the preceding pre-injection, the main injection is performed, and combustion is started when the pre-mixture in which the lean mixture and the rich mixture are unevenly distributed is formed, so the intake oxygen concentration is greatly increased in order to reduce NOx. Even in the lowered state, the rich air-fuel mixture is reliably ignited, and unburned HC due to poor ignition can be reduced.

  On the other hand, according to the present embodiment (the invention described in claim 4), by performing the preceding injection for distributing the lean air-fuel mixture at an early stage (a considerably early time), the air-fuel mixture obtained by the preceding injection is compressed top dead center. It is possible to prevent an equivalence ratio that is easy to burn before, to prevent the pre-injected fuel from being ignited early and to become a fire type at the injection timing of the main injection, and to suppress diffusive combustion of the main injected fuel.

  According to the present embodiment (the invention described in claim 4), since the intake oxygen concentration is greatly reduced, the combustion steepness of the rich mixture that is premixed and combusted can be reduced, and the rich mixture is further reduced. And lean mixture coexist, even if the premixed combustion of the rich mixture is steep, the slow combustion of the lean mixture can suppress the steepness of combustion as a total and reduce combustion noise .

  On the other hand, according to the present embodiment (the invention described in claim 4), the combustion of the lean mixture tends to be incomplete, but the relatively sharp combustion of the rich mixture cancels (lean). It is possible to prevent incomplete combustion (to promote combustion of the air-fuel mixture).

  According to the present embodiment (the invention described in claim 6), since the main injection is completed immediately before the compression top dead center, not only the combustion noise is reduced, but also the smoke can be reduced.

1 Engine 5 EGR valve (Intake oxygen concentration adjustment device)
15 Fuel injection valve 30 Engine control unit

Claims (6)

Inspiratory oxygen concentration detection / estimation means for detecting or estimating the inspiratory oxygen concentration;
An intake oxygen concentration adjustment device capable of adjusting the intake oxygen concentration;
In the first operating region, the first combustion mode is performed in which the intake oxygen concentration is set to a relatively small first predetermined value using the intake oxygen concentration adjusting device and combustion is mainly premixed combustion. 1 combustion mode execution means;
What is the premixed combustion in a state where the intake oxygen concentration is set to a second predetermined value larger than the first predetermined value using the intake oxygen concentration adjusting device in a second operation region adjacent to the first operation region? Second combustion mode execution means for performing a second combustion mode that is different combustion;
When the second operating region is switched to the first operating region, the detected or estimated intake oxygen concentration is reduced to a second value between the second predetermined value and the first predetermined value. (3) Pilot injection amount setting means for setting the fuel injection amount of the pilot injection so that the fuel injection amount is increased until the predetermined value is reached and then decreased as the intake oxygen concentration decreases;
A diesel engine combustion control device comprising: pilot injection execution means for performing pilot injection prior to main injection using the set pilot injection amount.   The second combustion mode is continued in a transition period until the intake oxygen concentration decreases from the second predetermined value and reaches the first predetermined value, and the intake oxygen concentration reaches the first predetermined value. 2. The diesel engine combustion control device according to claim 1, wherein the combustion mode is switched to the first combustion mode. The intake oxygen concentration adjusting device is an EGR device capable of adjusting an EGR rate,
The diesel engine combustion control apparatus according to claim 1, wherein the intake oxygen concentration estimating means estimates the intake oxygen concentration based on an actual EGR rate.   In the first combustion mode execution means, the first predetermined value is an intake oxygen concentration that does not cause a low-temperature oxidation reaction until the main injection is completed, and after performing the preceding injection prior to the main injection during the compression process 2. The combustion control apparatus for a diesel engine according to claim 1, wherein combustion is started when a pre-mixture in which lean mixture and rich mixture are unevenly distributed is formed by performing main injection.   5. The diesel engine combustion control apparatus according to claim 4, wherein the lean mixture is formed by the preceding injection, and the rich mixture is formed by main injection performed in the vicinity of the compression top dead center TDC.   The diesel engine combustion control apparatus according to claim 5, wherein the main injection is finished immediately before the compression top dead center.

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