JP2016166592A - Controller of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the combustion engine of fuel spray in a diesel engine.SOLUTION: In a combustion chamber 11b of an engine 10, fuel is injected from an injector 17, and the injection fuel is combusted. An ECU 40 includes: first calculation means of calculating reach timing at which fuel spray injected from the injector 17 reaches the wall surface of the combustion chamber 11b; second calculation means of calculating predetermined specific combustion timing between combustion start and combustion end of fuel spray; and fuel injection control means of controlling an injection form from the injector 17, on the basis of the difference between the reach timing and the specific combustion timing.SELECTED DRAWING: Figure 1

Description

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

  The fuel (mainly light oil) used in diesel engines has a large variation in properties, which affects the combustion characteristics in the combustion chamber due to the variation in properties. Therefore, conventionally, a technique has been proposed in which the cetane number of a fuel is detected as an indicator of the combustion characteristics of a fuel used in a diesel engine, particularly ignitability, and the target ignition timing is variably set based on the cetane number (Patent Document 1) reference). In this technique, it is described that the higher the cetane number of the fuel, the better the fuel state can be maintained by advancing the target ignition timing.

JP 2007-278119 A

  By the way, when fuel is injected from the fuel injection valve into the combustion chamber of a diesel engine, the fuel travels toward the wall surface around the combustion chamber, but the amount of fuel reaching the wall surface increases and the combustion region approaches the wall surface. If it is in an excessive state, there is a concern that an increase in cooling loss and an increase in exhaust emissions such as soot and HC may occur. In this regard, the existing technology does not take into account that the combustion region of the fuel is too close to the wall surface, and it is considered that there is room for examination.

  The present invention has been made in view of the above circumstances, and a main object thereof is to provide a control device for a diesel engine that can optimize the combustion state of fuel spray in the diesel engine.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The control device for a diesel engine according to the present invention includes a first calculation means for calculating the arrival time of the fuel spray injected from the fuel injection valve to the wall surface of the combustion chamber, and between the start of combustion of the fuel spray and the end of combustion. Based on a time difference between the second calculation means for calculating a predetermined specific combustion timing, the arrival time calculated by the first calculation means, and the specific combustion timing calculated by the second calculation means, a fuel injection valve And a fuel injection control means for controlling the injection mode.

  In considering the combustion state of fuel spray in a diesel engine, it is necessary to consider the relationship between the position of fuel spray in the combustion chamber and the combustion position, and in particular, the positional relationship with respect to the wall surface of the combustion chamber is considered to be important. In this regard, in the above-described configuration, the fuel spray injected from the fuel injection valve reaches the wall of the combustion chamber and the specific combustion timing determined in advance from the start of combustion of the fuel spray to the end of combustion are calculated. Thus, it is possible to grasp the temporal characteristics and the spatial characteristics regarding the combustion of the fuel spray in the combustion chamber. Then, by controlling the injection mode by the fuel injection valve based on the time difference between the arrival timing and the specific combustion timing, appropriate fuel injection control is performed in consideration of the relationship of the combustion position with respect to the wall surface of the combustion chamber. It becomes possible. As described above, the combustion state can be optimized in the diesel engine.

The block diagram which shows the outline | summary of the control system of a diesel engine. The figure which shows the state of fuel spray. A time chart showing changes in fuel injection rate, spray tip position, and heat generation rate. The time chart which shows the state which the combustion start time and the combustion peak time shifted | deviated. The time chart which shows the state from which the combustion gravity center time and the combustion end time shifted | deviated. The flowchart which shows the process sequence of fuel-injection control. The flowchart which shows the process sequence of fuel-injection control.

  Hereinafter, each embodiment which embodied the control apparatus which controls the diesel engine for vehicles is described. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals in the drawings, and the description of the same reference numerals is used.

(First embodiment)
First, with reference to FIG. 1, the outline | summary of the engine 10 which is a diesel engine is demonstrated. The engine 10 is, for example, an in-line four-cylinder diesel engine, and only one cylinder (cylinder) is shown in FIG. As shown in FIG. 1, the engine 10 includes a cylinder block 11, a piston 12, a cylinder head 13, an intake passage 14, an exhaust passage 15, an intake valve 16, an injector 17, an exhaust valve 18, a VVT 21, an EGR device 26, and a turbocharger 29. Etc.

  The cylinder block 11 is formed with four cylinders 11a. Each cylinder 11a accommodates a piston 12 in a reciprocable manner. A cylinder head 13 is assembled to the cylinder block 11. A cavity (concave portion) is formed on the upper surface of the piston 12, and a combustion chamber 11b is formed by the cavity.

  The intake passage 14 is formed as a passage in the intake manifold and the cylinder head 13 and is connected to each cylinder 11a. The camshafts 19A and 19B are rotated by the rotation of the crankshaft (not shown) of the engine 10. Each intake valve 16 is driven based on the rotation of the camshaft 19 </ b> A, and the intake air flows into the combustion chamber 11 b according to the drive of each intake valve 16. The VVT 21 (variable valve timing device) makes the opening / closing timing of the intake valve 16 variable by adjusting the rotational phase of the crankshaft and the camshaft 19A.

  The exhaust passage 15 is formed as a passage in the exhaust manifold and the cylinder head 13, and is connected to each cylinder 11a. Each exhaust valve 18 is driven based on the rotation of the camshaft 19B, and the exhaust is discharged from the combustion chamber 11b according to the driving of each exhaust valve 18.

  The common rail 20 (accumulation container) holds fuel in an accumulator state. The fuel is pressurized to a high pressure state by a fuel pump (not shown) and is pumped to the common rail 20. The injector 17 (fuel injection valve) injects fuel held in the accumulated pressure in the common rail 20 into the combustion chamber 11b. The injector 17 is a known electromagnetically driven or piezo driven valve that controls the valve opening period by controlling the fuel pressure in the control chamber that applies pressure to the nozzle needle in the valve closing direction. The valve opening period is controlled by the energization time of the electromagnetically driven or piezo driven actuator, and the longer the valve opening period of the injector 17, the greater the amount of injection.

  The EGR device 26 (exhaust gas recirculation device) includes an EGR passage 27 and an EGR valve 28. The EGR passage 27 connects the exhaust passage 15 and the intake passage 14. The EGR passage 27 is provided with an EGR valve 28 that opens and closes the EGR passage 27. The EGR device 26 introduces part of the exhaust gas in the exhaust passage 15 into the intake passage 14 in accordance with the opening degree of the EGR valve 28.

  In the intake stroke of the engine 10, air is sucked into the cylinder 11a through the intake passage 14, and the air is compressed by the piston 12 in the compression stroke. In the vicinity of the compression top dead center, fuel is injected into the cylinder 11a (inside the combustion chamber 11b) by the injector 17, and the fuel injected in the combustion stroke is self-ignited and burned. In the exhaust stroke, the exhaust in the cylinder 11 a is exhausted through the exhaust passage 15. Part of the exhaust gas in the exhaust passage 15 is introduced into the intake air in the intake passage 14 by the EGR device 26.

  The turbocharger 29 is, for example, a variable capacity turbocharger (supercharging means), and it is possible to adjust the output of the exhaust turbine by operating a variable nozzle, and thus to adjust the intake density in the engine 10. Yes.

  The engine 10 is provided with an in-cylinder pressure sensor 31. The cylinder pressure sensor 31 detects the pressure (cylinder pressure) in the cylinder 11a. The in-cylinder pressure sensor 31 does not need to be installed in all the cylinders 11a, and may be set in at least one cylinder 11a. A fuel tank (not shown) of the engine 10 is provided with a fuel density sensor 32, a kinematic viscosity sensor 33, and a fuel amount sensor 34. The fuel density sensor 32 detects the density of the fuel supplied to the injector 17. The fuel density sensor 32 detects the density of the fuel based on, for example, a natural vibration period measurement method. The kinematic viscosity sensor 33 is, for example, a capillary viscometer or a kinematic viscometer based on a thin wire heating method, and detects the kinematic viscosity of the fuel in the fuel tank. The fuel amount sensor 34 detects the amount of fuel in the fuel tank. The fuel density sensor 32 and the kinematic viscosity sensor 33 include a heater, and detect the density and kinematic viscosity of the fuel, respectively, in a state where the fuel is heated to a predetermined temperature by the heater.

  The ECU (Electric Control Unit) 40 is a known microcomputer including a CPU, a ROM, a RAM, an I / O, and the like, and corresponds to a control device that controls the engine 10. The ECU 40 is based on detection values of various sensors such as a crank angle sensor, a coolant temperature sensor, an accelerator opening sensor, an in-cylinder pressure sensor 31, a fuel density sensor 32, a kinematic viscosity sensor 33, and a fuel amount sensor 34, and the injector 17, VVT 21. The EGR device 26 and the like are controlled. Specifically, the control states of the injector 17, the VVT 21, and the EGR device 26 are adapted in accordance with the operating state of the engine 10 so that the fuel combustion state is optimal assuming a standard property fuel in advance. . The ECU 40 controls each device so as to achieve an adapted control state (normal combustion control) based on detection values of various sensors. The ECU 40 performs multi-stage injection including at least pilot injection and main injection by the injector 17.

  Further, the ECU 40 implements the functions of the first calculation means, the second calculation means, and the fuel injection control means by the CPU executing various programs stored in the ROM.

  By the way, the injector 17 has a plurality of injection holes at its tip, and the fuel spray injected from the injection holes proceeds toward the wall surface surrounding the combustion chamber 11b. Specifically, as shown in FIG. 2, the injector 17 injects fuel at the center of the cylinder, and the injected fuel spray F advances toward the peripheral edge where the maximum diameter of the combustion chamber 11 b is reached. In this case, when the piston 12 is near the top dead center, the distance from the injection position to the wall surface of the peripheral edge of the combustion chamber is L, and the separation distance from the injection position (injector tip) to the spray tip position reaches L. At that time, the fuel spray F reaches the wall surface of the combustion chamber 11b. Further, the fuel spray F is subjected to combustion by self-ignition accompanying compression in the process of traveling in the combustion chamber 11b.

  In this embodiment, the arrival timing of the fuel spray injected from the injector 17 to the wall surface of the combustion chamber 11b and the specific combustion timing determined in advance from the start of combustion of the fuel spray to the end of combustion are calculated and reached. The injection mode by the injector 17 is controlled based on the time difference between the timing and the specific combustion timing, and the details will be described below.

  First, the basic action during combustion of fuel spray will be described. FIG. 3 is a time chart showing the transition of the injection rate, spray tip position, and heat generation rate after the start of injection by the injector 17. In FIG. 3, the transition of the injection rate is shown as a change in speed when fuel is ejected from the nozzle hole, that is, a change in fuel injection speed.

  In FIG. 3, at timing t1, fuel injection of the injector 17 is started in response to an injection pulse (not shown), and the injection rate (fuel injection speed) increases accordingly. Further, the spray tip position gradually moves away from the injection position (injector tip). At timing t2, the fuel spray is ignited, and after timing t2, the heat generation rate increases as shown. In this case, the heat generation rate rises to a peak value at a stroke from the timing of ignition, and then turns down. Timing t1 is the timing for starting combustion, and timing t4 is the timing for ending combustion. The change in the heat generation rate is recognized as a change in the in-cylinder pressure detected by the in-cylinder pressure sensor 31.

  The spray tip position reaches the position of the distance L at timing t3, for example. That is, the timing t3 corresponds to the arrival time when the fuel spray reaches the wall surface of the combustion chamber 11b.

  The waveform representing the time change of the heat generation rate is a combustion waveform indicating the combustion state of the fuel spray, and according to this combustion waveform, it is determined in advance from the start of combustion of the fuel spray to the end of combustion (t1 to t4). It is possible to determine the specific combustion time. The area in the waveform corresponds to the amount of heat generated.

The specific combustion time includes at least one of the following times (1) to (4).
(1) Combustion start time (2) Combustion peak time (3) Combustion center-of-gravity time (4) Combustion end time Among these, the combustion center-of-gravity time is a time representing the center of gravity of the heat generated by the combustion of the fuel spray. In FIG. 3, ta is the combustion start timing (ignition timing), tb is the combustion peak timing, tc is the combustion center of gravity timing, and td is the combustion end timing.

  Among the above (1) to (4), the combustion start timing ta and the combustion peak timing tb belong to the period from the start of combustion to the combustion peak at which the heat generation rate becomes maximum, and this corresponds to the “first specific time”. . Further, the combustion center-of-gravity time tc and the combustion end time td are times related to the end of combustion, and this corresponds to the “second specific time”.

  It is conceivable that the timings ta to td of the above (1) to (4) are shifted to the advance side or the retard side due to the variation in fuel properties. When the times ta to td are shifted in this way, a time difference occurs between these times ta to td and the wall surface arrival time t3 when the fuel spray reaches the wall surface of the combustion chamber 11b. Therefore, in the present embodiment, any one of the above (1) to (4) is compared with the arrival time when the fuel spray reaches the wall surface of the combustion chamber 11b, and the injection mode by the injector 17 is based on the result. Is appropriately controlled.

  Incidentally, in the fuel, there are a mixture of components that are relatively easy to burn and components that are relatively difficult to burn. Incombustible components include burned burned gases. In this case, during the period from the start of combustion to the combustion peak, it is considered that variations in the combustion start timing ta and the combustion peak timing tb occur due to the influence of variations in components that are relatively flammable. In other words, when there is a variation in properties for components that are relatively flammable, as shown in FIG. 4, there is a variation in the state of heat generation at the beginning of combustion, and the combustion start timing ta with respect to the standard waveform indicated by the alternate long and short dash line. And combustion peak time tb shifts. Note that even if the combustion start timing ta is substantially the same, the combustion peak timing tb may be greatly delayed.

  Further, since the combustion end timing is easily affected by variations in components that are relatively incombustible, it is considered that variations in the combustion gravity center timing tc and the combustion end timing td occur due to the effects of variations in components that are relatively incombustible. In other words, when there is a variation in properties of components that are relatively difficult to burn, as shown in FIG. Or a combustion end timing td is generated.

  FIG. 6 is a flowchart showing a processing procedure of fuel injection control, and this processing is repeatedly performed by the ECU 40 at a predetermined cycle.

  In FIG. 6, in step S11, the fuel injection speed u0 of the nozzle hole portion, the air density ρa, and the spray angle α (see FIG. 2) are calculated as parameters related to fuel spray. For example, the fuel injection speed u0 is calculated from the equation (1), the air density ρa is calculated from the equation (2), and the spray angle α is calculated from the equation (3).

式（１）において、ρｆは燃料密度であり、Ｐｃはコモンレール２０内の燃料圧力（レール圧）であり、Ｐcyl（θinj）は燃料噴射期間におけるクランク角θinjに対する筒内圧であり、ｃは流量係数である。なお、燃料密度ρｆ、燃料噴射圧Ｐｃ、筒内圧Ｐcyl（θinj）は、それぞれ燃料密度センサ３２、コモンレール２０に設けられたレール圧センサ、筒内圧センサ３１による検出値として取得可能である。また、燃料噴射圧Ｐｃは、インジェクタ１７に内蔵された圧力センサの検出情報から取得することも可能である。

In equation (1), ρf is the fuel density, Pc is the fuel pressure (rail pressure) in the common rail 20, Pcyl (θinj) is the in-cylinder pressure with respect to the crank angle θinj during the fuel injection period, and c is the flow coefficient. It is. The fuel density ρf, the fuel injection pressure Pc, and the in-cylinder pressure Pcyl (θinj) can be acquired as detected values by the fuel density sensor 32, the rail pressure sensor provided on the common rail 20, and the in-cylinder pressure sensor 31, respectively. The fuel injection pressure Pc can also be obtained from detection information of a pressure sensor built in the injector 17.

  In equation (2), Pim is the intake manifold pressure, R is the gas constant, Tim is the intake manifold gas temperature, Mair is the intake average molecular weight, and V (θclose) is the cylinder at the intake valve closing timing. V (θinj) is a cylinder volume with respect to the crank angle θinj. The intake manifold pressure Pim and the intake manifold gas temperature Tim can be acquired as detection values by the intake manifold pressure sensor and the intake manifold gas temperature sensor, respectively. The intake average molecular weight Mair can be calculated based on the detected value of the air flow meter and the EGR opening. The cylinder volume V can be calculated based on the crank angle position.

  In equation (3), d0 is the nozzle hole diameter, μa is the intake viscosity coefficient, and μf is the fuel viscosity coefficient. The fuel viscosity coefficient μf can be calculated by multiplying the fuel density ρf detected by the fuel density sensor 32 and the kinematic viscosity ν detected by the kinematic viscosity sensor 33.

  Thereafter, in step S12, the spray tip position x with respect to time t with reference to the start timing of fuel injection based on the fuel injection speed u0, the air density ρa and the spray angle α calculated in step S11 using equation (4). (T) is calculated.

ただし、噴霧先端位置ｘ（ｔ）の算出手法は上記に限られない。

However, the calculation method of the spray tip position x (t) is not limited to the above.

  Thereafter, in step S13, the wall surface arrival time, which is the timing at which the fuel spray reaches the wall surface of the combustion chamber 11b, based on the spray tip position x (t) and the distance L from the injection position to the wall surface of the combustion chamber 11b. calculate.

  In step S14, the specific combustion timing is calculated based on the change waveform of the heat release rate, that is, the change waveform of the in-cylinder pressure. The specific combustion time is at least one of the combustion start time ta, the combustion peak time tb, the combustion gravity center time tc, and the combustion end time td as described above. Among these, the combustion start timing ta, the combustion peak timing tb, and the combustion end timing td are obtained by sequentially monitoring changes in the heat generation rate, that is, changes in the in-cylinder pressure. Further, the combustion center-of-gravity timing tc is obtained from the heat generation rate in the combustion period from the start of combustion to the end of combustion using, for example, the following equation (5).

式（５）において、ｘ（ｔ）は時間ｔにおける熱発生率、Δｔは熱発生率のサンプリング時間を示す。

In equation (5), x (t) represents the heat generation rate at time t, and Δt represents the heat generation rate sampling time.

  In addition, the calculation of the wall surface arrival time and the specific combustion time in steps S11 to S14 may be performed at one point or a plurality of points in the idle state under a state where the vehicle is traveling steadily. Moreover, it is good to carry out whenever the travel distance becomes a predetermined distance (for example, 10 km) or every time a predetermined time elapses.

  In step S15, a time difference ΔT between the fuel spray wall arrival time and the specific combustion timing is calculated. In subsequent step S16, whether the fuel spray combustion position is too close to the wall surface of the combustion chamber 11b based on the time difference ΔT. Determine whether or not. This process is also a process for determining that the combustion ratio after the spray tip reaches the combustion chamber wall surface is greater than or equal to a predetermined value.

  At this time, if the time difference ΔT is within a predetermined range determined based on the combustion waveform of the standard property, it is determined that the combustion position of the fuel spray is not too close to the wall surface of the combustion chamber 11b, and this processing is performed as it is. finish. If the time difference ΔT is not within the predetermined range, it is determined that the fuel spray combustion position is too close to the wall surface of the combustion chamber 11b, and the process proceeds to step S17. The predetermined range is individually determined depending on which time the specific combustion timing is. The predetermined range may be set variably based on the rotation speed and load of the engine 10.

  More specifically, in step S16, it is determined whether or not the time difference between the wall surface arrival time and the combustion start time ta is within a predetermined range, and whether or not the time difference between the wall surface arrival time and the combustion peak time tb is within a predetermined range. In addition, it is determined whether or not the time difference between the wall surface arrival time and the combustion center-of-gravity time tc is within a predetermined range, and whether or not the time difference between the wall surface arrival time and the combustion end time td is within a predetermined range. When a plurality of condition determinations are performed, step S16 may be positively determined when two or more conditions are satisfied.

  For example, when the combustion start timing ta and the combustion peak timing tb are shifted to the retard side as shown by the solid line in FIG. 4, step S16 is affirmed when the time difference ΔT is outside the predetermined range. Further, as indicated by the solid line in FIG. 5, when the combustion center-of-gravity timing tc and the combustion end timing td are shifted to the retard side, the time difference ΔT is outside the predetermined range, so that step S16 is affirmed.

  In step S17, it is determined whether or not it is possible to subdivide pilot injection in multistage injection. At this time, it is determined based on the number of pilot injection stages and the interval time whether or not the number of injection stages can be increased while the interval time is narrowed. If the pilot injection can be subdivided, the process proceeds to step S18.

  In step S18, the pilot injection is subdivided to keep the combustion position of the fuel spray away from the wall surface. At this time, the number of pilot injection stages is increased by 1, and the interval time is adjusted accordingly. Specifically, the number of injection stages is increased by 1 after fixing the total injection amount of pilot injection. In addition, the interval time is shortened so that the period from the first stage pilot injection to the start of the main injection remains unchanged.

  By thus subdividing the pilot injection, the fuel spray at each injection stage is prevented from approaching the wall surface of the combustion chamber 11b. That is, the fuel spray stays in the vicinity of the injector tip. Thereby, the ignition source of combustion of the main injection can be shifted to a position closer to the center of the combustion chamber 11b.

  Thereafter, in step S19, combustion correction control is performed. For example, as the combustion correction control, correction control regarding the injection timing of the main injection, the injection pressure, the intake air density, and the O2 concentration is performed in order to reduce the combustion rate after the spray tip reaches the combustion chamber wall surface. More specifically, the injection timing of the main injection is advanced by shifting the injection pulse to the advance side. Further, the injection pressure is lowered by controlling the discharge amount of the fuel pump, and the reach distance of the spray tip at the same time is shortened. By adjusting the throttle by the variable nozzle of the turbocharger 29, the intake density is increased and the reach distance of the spray tip at the same time and injection amount is shortened. The combustion time is shortened by reducing the EGR opening and increasing the O2 concentration. Any one of these processes may be performed.

  The combustion correction control in step S19 can also be changed depending on whether or not the pilot injection subdivision control in step S18 is performed.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  In considering the combustion state of the fuel spray in the engine 10 which is a diesel engine, it is necessary to consider the relationship between the position of the fuel spray in the combustion chamber 11b and the combustion position, and in particular, the positional relationship with respect to the wall surface of the combustion chamber 11b. It will be important. In this regard, in the above configuration, the fuel spray injected from the injector 17 reaches the wall surface of the combustion chamber 11b and the specific combustion time from the start of combustion to the end of combustion is calculated, thereby calculating the inside of the combustion chamber 11b. It is possible to grasp the temporal and spatial characteristics of fuel spray combustion in Japan. Then, by controlling the injection mode by the injector 17 based on the time difference between the wall surface arrival time and the specific combustion time, appropriate fuel injection control is performed in consideration of the relationship of the combustion position with respect to the wall surface of the combustion chamber 11b. It becomes possible to do. As described above, the combustion state can be optimized in the diesel engine.

  According to the time difference between the wall surface arrival time and the specific combustion time, it is possible to determine that the combustion position in the combustion chamber 11b is too close to the wall surface of the combustion chamber 11b. When it is determined that the combustion position is too close to the wall surface of the combustion chamber 11b, the injection state by the injector 17 is controlled so as to keep the combustion position away from the wall surface of the combustion chamber 11b, thereby optimizing the combustion state. Can be realized.

  As a control of the injection mode that is performed to keep the combustion position away from the wall surface of the combustion chamber 11b, the subdivision control of the pilot injection is performed. In this case, the fuel spray by the pilot injection stays at a position near the center of the combustion chamber, and the ignition source of main combustion can be concentrated in the vicinity of the center of the combustion chamber 11b. As a result, it is possible to suppress the ignition delay, and it is possible to realize a combustion state equivalent to that of the normal fuel even when the characteristics are unintentionally varied (for example, when a low cetane number fuel is used).

  The first specific time (combustion start time, combustion peak time) in the period from the start of combustion to the combustion peak where the heat generation rate is maximum is calculated as the specific combustion time, and the fuel spray wall surface arrival time and the first specific time The injection mode by the injector 17 is controlled based on the time difference. For this reason, it is possible to perform appropriate fuel injection control in consideration of variations in components that are relatively flammable.

  Also, the second specific time (combustion center of gravity time, combustion end time) related to the end of combustion is calculated as the specific combustion time, and the injection mode by the injector 17 is based on the time difference between the fuel spray wall surface arrival time and the second specific time. To control. For this reason, it is possible to perform appropriate fuel injection control in consideration of variations in components that are relatively difficult to burn.

(Other embodiments)
You may change the said embodiment as follows, for example.

  The fuel injection control may be performed as shown in FIG. FIG. 7 is performed by the ECU 40 in place of the process of FIG. 6, but the process of steps S11 to S14 is common and is not shown.

  In FIG. 7, in step S21, it is determined whether or not the current engine operating state is in a predetermined low load range. This process determines whether the engine operating state is in a predetermined low load region or a high load region on the higher load side. At this time, for example, it is determined that the vehicle is in the low load region when the vehicle is in the idle operation state or the operation state near the idle. When the vehicle is in the middle load state in addition to the low load state near the idle, it may be determined that the vehicle is in the low load region. It is also possible to carry out load determination in consideration of the engine rotation speed. If step S21 is YES, the process proceeds to step S22, and if NO, the process proceeds to step S23. In step S22, a time difference ΔT between the combustion start timing ta or the combustion peak timing tb, which is the first specific timing, and the fuel spray wall surface arrival timing is calculated. In step S23, a time difference ΔT with respect to the fuel spray wall surface arrival time for the combustion center-of-gravity time tc or the combustion end time td, which is the second specific time, is calculated.

  Subsequent processing (S16 to S19) after the calculation of the time difference ΔT is the same as that in FIG. 6, and the determination of the fuel spray combustion position and the pilot injection subdivision control and the combustion correction control based on the determination result are performed as described above. Is done.

  According to the said structure, there exist the following effects. In short, when comparing the low load state and the high load state of the engine 10, it is considered that the combustion environment in the combustion chamber 11b is generally better in the high load state. The reason why the combustion environment is improved is that the amount of EGR gas is reduced in a high load state and the filling rate of fresh air is increased by supercharging or the like. Therefore, in a high load state, even if there is a variation in components that are relatively flammable, it is considered that the effect is less likely to occur. In this regard, when the load of the engine 10 is in a low load region, determination of the fuel spray combustion position is based on the time difference between the fuel spray wall surface arrival time and the first specific time (combustion start time, combustion peak time). When the load of the engine 10 is in a high load range, based on the time difference between the fuel spray wall surface arrival time and the second specific time (combustion gravity center time, combustion end time), The fuel spray combustion position is determined and the injection mode is controlled. Therefore, it is possible to perform proper fuel injection control while taking into account the occurrence of property variations.

  In FIG. 7, the determination of the combustion position of the fuel spray and the control of the injection mode may be performed only when the engine operating state is in a predetermined low load range. In this case, the determination of the combustion position of the fuel spray and the control of the injection form are not performed in the high load range.

  As an index for knowing that the combustion position of the fuel spray is too close to the wall surface of the combustion chamber 11b, in addition to the above-mentioned combustion start time (ignition time), combustion peak time, combustion center of gravity time, combustion end time, combustion start Can be used in consideration of the length Tx of the combustion period from the end of combustion to the end of combustion. That is, as shown in FIG. 3, when the length of the combustion period is Tx and the time difference between the combustion start time ta (t2) as the specific combustion time and the wall surface arrival time t3 is Ty, the length of the combustion period Tx The ratio (Ty / Tx) of the time difference Ty with respect to is calculated. Then, based on the Ty / Tx, it is possible to determine whether or not the combustion position of the fuel spray is too close to the wall surface of the combustion chamber 11b, and based on the determination result, the injection mode by the injector 17 can be controlled. It is.

  Further, when the time difference between the combustion end timing td (t4) as the specific combustion timing and the wall surface arrival timing t3 is Tz, the ratio (Tz / Tx) of the time difference Tz to the length Tx of the combustion period is calculated. Then, based on the Tz / Tx, it is possible to determine whether or not the combustion position of the fuel spray is too close to the wall surface of the combustion chamber 11b, and based on the determination result, the injection mode by the injector 17 can be controlled. It is.

  -In the above embodiment, when subdividing the fuel injection in the multi-stage injection, the subdivision of the pilot injection was performed. However, this may be changed and the fuel injection including the main injection may be subdivided. Good.

  As the control of the injection mode by the injector 17, at least one of the reduction of the injection pressure and the advance of the injection timing may be performed without performing the subdivision of the fuel injection at the time of multistage injection.

  DESCRIPTION OF SYMBOLS 10 ... Engine (diesel engine), 11b ... Combustion chamber, 17 ... Injector (fuel injection valve), 40 ... ECU (1st calculation means, 2nd calculation means, fuel injection control means).

Claims (7)

A control device (40) for controlling injection of fuel into the combustion chamber (11b) by the fuel injection valve (17) in the diesel engine (10),
First calculation means for calculating the arrival time of the fuel spray injected from the fuel injection valve to the wall surface of the combustion chamber;
A second calculation means for calculating a predetermined specific combustion time between the start of combustion of the fuel spray and the end of combustion;
Fuel injection control means for controlling an injection mode by the fuel injection valve based on a time difference between the arrival time calculated by the first calculation means and the specific combustion time calculated by the second calculation means;
A control device for a diesel engine, comprising: Determination means for determining that the combustion position of the fuel spray is too close to the wall surface of the combustion chamber based on a time difference between the arrival time and the specific combustion time;
The fuel injection control means controls the injection mode by the fuel injection valve so as to keep the combustion position away from the wall surface when the determination means determines that the combustion position is too close to the wall surface of the combustion chamber. The diesel engine control device according to claim 1.   The fuel injection control means is configured to divide multi-stage injection by the fuel injection valve so as to keep the combustion position away from the wall surface when the determination means determines that the combustion position is too close to the wall surface of the combustion chamber. The control device for a diesel engine according to claim 2, wherein fuel injection is subdivided by increasing the number of stages. The second calculation means calculates the first specific time in the period from the start of combustion to the combustion peak at which the heat generation rate is maximum as the specific combustion time,
4. The control of a diesel engine according to claim 1, wherein the fuel injection control unit controls an injection mode by the fuel injection valve based on a time difference between the arrival time and the first specific time. 5. apparatus. The second calculation means calculates a second specific time related to the end of combustion as the specific combustion time,
The diesel engine control according to any one of claims 1 to 4, wherein the fuel injection control means controls an injection mode by the fuel injection valve based on a time difference between the arrival time and the second specific time. apparatus. The second calculation means calculates, as the specific combustion time, a first specific time in a period from the start of combustion to a combustion peak at which the heat generation rate becomes maximum, and a second specific time related to the combustion end time,
The fuel injection control means controls the injection mode by the fuel injection valve based on the time difference between the arrival time and the first specific time when the load of the diesel engine is in a predetermined low load range, When the load of the diesel engine is in a high load range higher than the low load range, the injection mode by the fuel injection valve is controlled based on the time difference between the arrival time and the second specific time. The control apparatus of the diesel engine of any one of Claims 1 thru | or 3. The second calculating means calculates a combustion start time or a combustion end time as the specific combustion time,
The fuel injection control means controls an injection mode by the fuel injection valve based on a ratio of a time difference between the arrival timing and the specific combustion timing with respect to a length of a combustion period from the start of combustion of the fuel spray to the end of combustion. The control device for a diesel engine according to any one of claims 1 to 3.

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