JP2016070191A - Fuel control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further optimize the combustion of main injection and engine performance by securing a proper amount of a calorific value of frontstage injection.SOLUTION: In an engine in which a cavity 10 which is recessed to a direction separating from a bottom face of a cylinder head 5 is formed at a piston crown face 4a, when performing main injection Om, and frontstage injections Qpi, Qpr which inject a smaller amount of fuel than that of the main injection Qm prior to the main injection Qm, a spilt amount of an injection amount of the frontstage injection which is spilt to the outside of the cavity 10 is calculated, and the injection amount of the frontstage injection is decided on the basis of the spilt amount and a target value of a calorific value which is generated in a cylinder 2 by the combustion of fuel which is injected by the frontstage injection.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an engine fuel control device including an injection device capable of injecting fuel into a cylinder and an injection control means for controlling the injection device.

  Conventionally, in order to perform combustion for generating engine torque more reliably and efficiently, main injection that injects main fuel near the compression top dead center, and injection of main injection before this main injection Implementation of pre-injection in which an amount of fuel smaller than the amount is injected is performed. That is, if the pre-stage injection is carried out, the fuel and air can be mixed and the fuel can be burned efficiently, and the temperature of the cylinder is increased by the combustion of the pre-stage injection to increase the temperature of the main injected fuel. Ignition can be improved.

  Here, depending on the heat generation amount of the front injection, the combustion state of the main injection cannot be made appropriate, and there is a possibility that proper engine performance cannot be ensured. Specifically, when the amount of heat generated by the front-stage injection is large, the main-injected fuel is ignited earlier than the appropriate time, resulting in an increased amount of soot, and the heat generated by the front-stage injection. When the amount is small, the temperature pressure in the cylinder cannot be sufficiently increased by the pre-stage injection, and problems such as deterioration of the ignitability of the main injected fuel occur.

  On the other hand, for example, in Patent Document 1, a target value for the heat generation amount of the front-stage injection is determined according to the start timing so that the start timing of combustion by the main injection becomes an appropriate time, and the target value is set to this target value. Accordingly, an apparatus for determining the injection amount of the pre-stage injection is disclosed.

JP 2009-185628 A

  In the apparatus disclosed in Patent Document 1, the target value of the heat generation amount of the front-stage injection is determined so that the start timing of the combustion by the main injection becomes an appropriate time. If the value is controlled, the combustion state of the main injection, and thus the engine performance can be made appropriate.

  However, the inventors of the present application have found that even when this device is used, the combustion state of the main injection cannot be made appropriate and proper engine performance may not be ensured. Specifically, in this device, the injection amount of the front-stage injection is determined only based on the target value of the heat generation amount of the front-stage injection. However, even if the determined injection amount is injected, the heat generation amount of the front-stage injection is not increased. There are cases where the target value is not reached and combustion by the pre-stage injection and the main injection cannot be brought into an appropriate state.

  The present invention has been made in view of the circumstances as described above, and is an engine fuel control apparatus that can ensure the proper amount of heat generated by the pre-injection to make the combustion of the main injection and the engine performance more appropriate. The purpose is to provide.

  As a result of diligent research on the above problems, the inventors of the present invention have found that in an engine in which a cavity recessed in the direction away from the bottom surface of the cylinder head is formed on the piston crown surface of the engine, a part of the injection amount of the front injection is from this cavity. It was found that it spilled outwards and diffused, and did not contribute to combustion.

  The present invention has been made based on this finding, and an engine fuel control device comprising an injection device capable of injecting fuel into a combustion chamber formed in a cylinder, and an injection control means for controlling the injection device. In the engine, the piston crown surface is formed with a cavity that is recessed in a direction away from the bottom surface of the cylinder head. Before, the injection device performs the pre-injection for injecting the fuel smaller than the main injection amount into the cylinder, and the pre-injected fuel burns based on the operating conditions. The target pre-stage heat generation amount determining means for determining the target pre-stage heat generation amount, which is the target value of the heat generation amount generated in the combustion chamber, and the outside of the cavity among the injection amounts of the pre-stage injection. Spill amount calculating means for calculating the spill amount, and pre-stage injection amount determining means for determining the injection amount of the pre-stage injection based on the calculated spill amount and the calculated target pre-stage heat generation amount, When the pre-stage injection is performed, the injection amount determined by the pre-stage injection amount determining means is caused to be injected by the injection device (claim 1).

  According to the present invention, as described above, in an engine in which a cavity that is recessed in the direction away from the bottom surface of the cylinder head is formed on the piston crown surface, the amount of spillage that spills outside the cavity is calculated out of the injection amount of the pre-stage injection. However, the injection amount of the pre-stage injection is determined based on the spill amount and the target pre-stage heat generation amount that is the target value of the heat generation amount by the pre-stage injection, and there is an injection amount that does not contribute to combustion by spilling out from the cavity. Since the injection amount of the front injection is determined in consideration, it is possible to secure an appropriate amount of heat generation of the front injection, thereby making it possible to more surely optimize the combustion state of the combustion by the main injection and thus the engine performance. it can.

  Here, as the injection pressure of the upstream injection is high and the distance that the fuel injected by the upstream injection reaches is longer, the amount of fuel scattered outside the cavity, that is, the amount of spillage increases, and the injection timing of the upstream injection is the advance side. The distance between the cavities and the cavity increases, and the amount of fuel scattered outside the cavities, that is, the amount of spillage increases.

  Therefore, in the present invention, the spill amount calculating means preferably calculates the spill amount as the injection pressure of the preceding injection is higher and the injection timing of the preceding injection is on the advance side. .

  In this way, it is possible to more accurately calculate the amount of spillage and, therefore, the injection amount of the pre-stage injection, and to make the combustion state of the combustion by the main injection and hence the engine performance more appropriate.

  In the present invention, the preceding injection amount determining means includes combustion efficiency calculating means for calculating the combustion efficiency of the fuel injected by the preceding injection based on the spill amount, and the calculated combustion efficiency as the combustion efficiency. Combustion efficiency correction means for correcting the temperature according to at least one of the wall surface temperature of the chamber, the temperature of the gas in the combustion chamber, the oxygen concentration in the combustion chamber, and the pressure in the combustion chamber, It is preferable to determine the injection amount of the pre-stage injection based on the target pre-stage injection heat generation amount.

  In this way, in addition to the amount of spillage, the state of the combustion chamber (the wall temperature of the combustion chamber, the temperature of the gas in the combustion chamber, the oxygen concentration in the combustion chamber, the pressure in the combustion chamber) that affects the amount of heat generated by the pre-stage injection Accordingly, the injection amount of the front-stage injection can be calculated more appropriately, and the combustion state of the combustion by the main injection and thus the engine performance can be made more appropriate.

  In the present invention, the injection control means performs the pre-stage injection in two or more times, and the target pre-stage heat generation amount determining means generates the heat generation amount generated in the combustion chamber by all the pre-stage injections. Is calculated as the target pre-stage heat generation amount, the spill amount calculation means calculates the spill amount of the first-stage injection performed first, and the pre-stage injection amount determination means is the target pre-stage heat generation amount and 2 It is preferable to determine the injection amount of the first-stage injection to be performed first based on the injection amount of the first-stage injection after the first time and the spill amount.

  According to this configuration, since the injection amount is determined based on the spill amount only for the first injection in which the amount of fuel spilling out of the cavity is the largest among the pre-stage injections, the injection amount of the pre-stage injection is taken into account. It is possible to simplify the calculation procedure of the injection amount while setting the value to an appropriate value and making the combustion state of the main injection combustion, and thus the engine performance appropriate.

It is a figure showing the whole diesel engine system composition concerning one embodiment of the present invention. It is sectional drawing which expands and shows a part of engine main body. It is a partially expanded sectional view of a piston. It is a top view of a piston. It is a block diagram which shows the control system of an engine. It is a figure which shows the switching area | region of a combustion mode. (A) It is a figure which shows the example of the injection pattern and heat release rate of diffusion combustion mode. (B) It is a figure which shows the other example of the injection pattern of a diffusion combustion mode, and a heat release rate. (B) It is a figure which shows the example of the injection pattern of a premix combustion mode, and a heat release rate. It is the flowchart which showed the flow of the whole control procedure of the injection system. It is the flowchart which showed the flow of the whole control procedure of the injection system. It is a figure for demonstrating the amount of spillage. It is the graph which showed the relationship between injection timing, injection pressure, and the amount of spillage. It is the graph which showed the relationship between the amount of spillage and combustion efficiency.

(1) Overall Configuration of Engine System FIG. 1 is a diagram showing an overall configuration of a diesel engine system according to an embodiment of the present invention. The diesel engine shown in the figure is a four-cycle diesel engine mounted on a vehicle as a driving power source. Specifically, this diesel engine has an engine body 1 that is driven by the supply of fuel mainly composed of light oil having a plurality of cylinders 2 and intake air for introducing combustion air into the engine body 1. A passage 30, an exhaust passage 40 for discharging exhaust gas (combustion gas) generated in the engine body 1, an EGR device 50 for returning a part of the exhaust gas passing through the exhaust passage 40 to the intake passage 30, And a turbocharger 60 driven by exhaust gas passing through the exhaust passage 40.

  In the intake passage 30, an air cleaner 31, a compressor 61 of the turbocharger 60, a throttle valve 36, an intercooler 35, and a surge tank 37 are provided in this order from the upstream side. On the downstream side of the surge tank 37, there are provided independent passages communicating with the cylinders 2 individually, and the gas in the surge tank 37 is distributed to the cylinders 2 through the independent passages.

  The exhaust passage 40 is provided with a turbine 62 of the turbocharger 60 and an exhaust purification device 41 in order from the upstream side.

  In the turbocharger 60, the turbine 62 rotates in response to the energy of the exhaust gas flowing through the exhaust passage 40, and the compressor 61 rotates in conjunction with this to compress the air flowing through the intake passage 30 (supercharging). )

  The intercooler 35 is for cooling the air compressed by the compressor 61.

  The throttle valve 36 opens and closes the intake passage 30. However, in this embodiment, the engine is basically fully opened or maintained at a high opening degree close to that during operation of the engine, and is closed only when necessary, such as when the engine is stopped, to block the intake passage 30.

  The exhaust purification device 41 is for purifying harmful components in the exhaust gas. In the present embodiment, the exhaust purification device 41 includes an oxidation catalyst 41a that oxidizes CO and HC in the exhaust gas, and a DPF 41b that collects soot (soot) in the exhaust gas.

  The EGR device 50 is for recirculating exhaust gas to the intake side. In the present embodiment, the EGR device 50 includes a high-pressure side EGR device (hereinafter referred to as HP_EGR device) 51, a low-pressure side EGR device (hereinafter referred to as LP_EGR device), and 52.

  The HP_EGR device 51 includes an HP_EGR passage 51a that connects a portion of the exhaust passage 40 upstream of the turbine 62 and a portion of the intake passage 30 downstream of the intercooler 35, and HP_EGR that opens and closes the HP_EGR passage 51a. A valve 51b is provided to recirculate relatively high-pressure exhaust gas discharged to the exhaust passage 40 (hereinafter sometimes referred to as high-pressure EGR gas) to the intake side.

  On the other hand, the LP_EGR device 52 opens and closes an LP_EGR passage 52a that connects a portion of the exhaust passage 40 downstream of the DPF 41b and a portion of the intake passage 30 between the air cleaner 31 and the compressor 61, and opens and closes the LP_EGR passage 52a. And an LP_EGR valve 52b that recirculates relatively low-pressure exhaust gas (hereinafter sometimes referred to as low-pressure EGR gas) discharged to the exhaust passage 40 to the intake side. An EGR cooler 52c for cooling the low-pressure EGR gas passing through the passage 52a is provided on the upstream side (exhaust passage 40 side) of the LP_EGR passage 52a with respect to the LP_EGR valve 52b.

(2) Configuration of Engine Body FIG. 2 is an enlarged cross-sectional view showing a part of the engine body 1. As shown in FIG. 2 and FIG. 1 above, the engine body 1 is accommodated in a cylinder block 3 in which a cylinder 2 extending in the vertical direction is formed, and in the cylinder 2 so as to be able to reciprocate (vertically move). A piston head 4, a cylinder head 5 provided so as to cover the end surface (upper surface) of the cylinder 2 from the side facing the crown surface 4 a of the piston 4, and a lower side of the cylinder block 3 for storing lubricating oil. And an oil pan 6 disposed.

  The piston 4 is connected to a crankshaft 7 that is an output shaft of the engine body 1 via a connecting rod 8. A combustion chamber 9 is formed above the piston 4, and in this combustion chamber 9, fuel injected from an injector 20 described later is diffusely burned while being mixed with air. The piston 4 reciprocates and the crankshaft 7 rotates about the central axis due to the expansion energy associated with the combustion.

  Here, the geometric compression ratio of the engine body 1, that is, the ratio of the combustion chamber volume when the piston 4 is at the bottom dead center to the combustion chamber volume when the piston 4 is at the top dead center is 12 or more and 15 The following is set (for example, 14). This geometric compression ratio of 12 or more and 15 or less is a considerably low value for a diesel engine. This is aimed at improving emission performance and thermal efficiency by suppressing the combustion temperature.

  The cylinder head 5 has an intake port 16 for introducing the air supplied from the intake passage 30 into the combustion chamber 9, and an exhaust port 17 for leading the exhaust gas generated in the combustion chamber 9 to the exhaust passage 40. An intake valve 18 for opening and closing the opening on the combustion chamber 9 side of the intake port 16 and an exhaust valve 19 for opening and closing the opening on the combustion chamber 9 side of the exhaust port 17 are provided.

  An injector (injection device) 20 that injects fuel into the combustion chamber 9 is attached to the cylinder head 5. The injector 20 is attached in such a posture that the tip end portion 21 a on the piston 4 side faces the center portion of the cavity 10. The injector 20 is connected to a pressure accumulation chamber (not shown) such as a common rail via a fuel flow path. High pressure fuel pressurized by a fuel pump (not shown) is stored in the pressure accumulating chamber, and the injector 20 receives fuel supplied from the pressure accumulating chamber and injects fuel into the combustion chamber 9. Between the fuel pump and the pressure accumulating chamber, a fuel pressure regulator (not shown) for changing the pressure in the pressure accumulating chamber, that is, the injection pressure that is the pressure of the fuel injected from the injector 20 is provided.

  A cavity 10 is formed in the crown surface 4a of the piston 4 so that a region including the center thereof is recessed on the side opposite to the cylinder head 5 (downward). The cavity 10 is formed to have a volume that occupies most of the combustion chamber 9 when the piston 4 rises to the top dead center.

  3 and 4 are an enlarged cross-sectional view and a plan view showing the periphery of the combustion chamber 9 in an enlarged manner. In FIG. 3 and FIG. 4, the symbol F indicates the spray of fuel injected from the injector 20. FIG. 4 shows a state where the piston 4 is at the top dead center.

  As shown in these drawings, in this embodiment, the injector 20 is mounted coaxially with the cylinder 2 (so that the central axis of the injector 20 and the central axis of the cylinder 2 coincide). Further, as the injector 20, a multi-hole type injector in which a plurality of nozzle holes 22 are formed at the tip end portion 21a is used. The injection holes 22 are arranged so as to be arranged at substantially equal intervals in the circumferential direction. By passing through the injection holes 22, fuel is radially emitted from the injector 20 into the combustion chamber 9 in a plan view. Be injected.

  As shown in FIGS. 3 and 4, the cavity 10 is a so-called reentrant type cavity. That is, the wall surface forming the cavity 10 includes a substantially mountain-shaped central raised portion 11, a peripheral concave portion 12 that is formed on the radially outer side of the piston 4 with respect to the central raised portion 11, and a peripheral concave portion 12 and a piston. And a lip portion 13 having a circular shape in plan view formed between the four crown surfaces 4a.

  The central raised portion 11 is raised so as to be closer to the injector 20 toward the center side of the cavity 10, and the top of the raised portion is formed immediately below the tip end portion 21 a of the injector 20. The peripheral concave portion 12 is continuous with the central raised portion 11 and is formed to have an arc shape that is recessed in the radially outer side of the piston 4 in a sectional view. The lip portion 13 is continuous with the peripheral concave portion 12 and is formed to have an arc shape that protrudes radially inward of the piston 4 in a sectional view.

  The cavity 10 having the above-described configuration as a whole has a constricted cross-sectional shape in which the opening area decreases as the distance from the crown surface 4a of the piston 4 decreases. Such a reentrant type cavity 10 mainly sprays the fuel spray F to the peripheral recess 12 and the central bulge 11 when a relatively large amount of fuel is injected, particularly in an operation region of a medium load or higher of the engine. Since the function of reversing from the radially outer side to the inner side (center side of the cavity 10) is exhibited, it is advantageous for promoting the mixing of the fuel.

(3) Control System (3-1) System Configuration FIG. 5 is a block diagram showing an engine control system. As shown in the figure, the diesel engine of the present embodiment is comprehensively controlled by a PCM (powertrain control module) 70. As is well known, the PCM 70 is a microprocessor including a CPU, a ROM, a RAM, and the like.

  The PCM 70 is electrically connected to various sensors for detecting the operating state of the engine.

  For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects a rotation angle (crank angle) and a rotation speed of the crankshaft 7. The crank angle sensor SN1 outputs a pulse signal in accordance with the rotation of a crank plate (not shown) that rotates integrally with the crankshaft 7. Based on the pulse signal, the rotation angle and the rotation speed of the crankshaft 7 are output. That is, the engine speed is specified.

  In the intake passage 30, in the vicinity of the air cleaner 31 (the portion between the air cleaner 31 and the connection portion of the LP_EGR passage 52 a), the amount of air (fresh air amount) taken into each cylinder 2 through the air cleaner 31 is detected. An airflow sensor SN2 is provided.

  The surge tank 37 is provided with an intake manifold temperature sensor SN3 that detects the temperature of the gas in the surge tank 37, that is, the gas sucked into each cylinder 2.

  An intake manifold pressure sensor SN4 that detects the pressure of the air passing through this portion and the intake air taken into the cylinder 2 is provided in the portion of the intake passage 30 downstream of the intercooler 35.

  The engine body 1 is provided with a water temperature sensor SN5 that detects the temperature of cooling water that cools the engine body.

  A fuel pressure sensor SN <b> 6 that detects the pressure in the pressure accumulation chamber, that is, the injection pressure of the injector 20, is provided in the pressure accumulation chamber that supplies fuel to the injector 20.

  In addition, the vehicle is provided with an accelerator opening sensor SN7 that detects the opening of an accelerator pedal (accelerator opening) that is operated by the driver and that is not shown.

  The PCM 70 controls each part of the engine while executing various determinations and calculations based on input signals from the various sensors. That is, the PCM 70 is electrically connected to the injector 20, the throttle valve 36, the fuel pressure regulator, the HP_EGR valve 51b, the LP_EGR valve 51c, and the like. The control signal is output.

(3-2) Intake System Control The flow of intake system control by the PCM 70 in the present embodiment will be briefly described.

  The PCM 70 determines a target torque that is a target value of the engine torque based on the accelerator opening (detected value of the accelerator opening sensor SN7), and is specified by the target torque and the engine speed (detected value of the crank angle sensor SN1). The required total injection amount that is a basic value of the total amount of fuel injected from the injector 20 into the combustion chamber 9 is determined based on the above. For example, the PCM 70 is a value corresponding to the accelerator opening or the like from a map of the accelerator opening and the target torque set in advance and stored, or from a map of the target torque, the engine speed and the required total injection amount. The above values are determined by extracting.

  Then, the PCM 70 determines the target intake oxygen concentration that is the target value of the oxygen concentration in the gas sucked into the cylinder 2 and the target value of the gas temperature sucked into the cylinder 2 based on the required total injection amount and the engine speed. The target intake air temperature and the EGR control mode (LP_EGR51 or HP_EGR52 are activated) are determined, and from the determined contents, the supercharging pressure that is the pressure of the gas sucked into the cylinder 2 and HP_EGR51 are determined. The amount of high pressure EGR gas that is the amount of exhaust gas recirculated to the intake passage 30 and the amount of low pressure EGR gas that is the amount of exhaust gas recirculated to the intake passage 30 are determined by LP_EGR52, so that this supercharging pressure and each EGR gas amount are realized. In addition, the throttle valve 36, the HP_EGR valve 51b, and the LP_EGR valve 51c are controlled.

(3-3) Control of Injection System Next, control of the injection system by the PCM 70 in this embodiment will be described.

(3-3-1) Combustion Mode and Injection Pattern FIG. 6 is a diagram showing a combustion mode according to the operating state of the engine. As shown in FIG. 6, in this embodiment, the combustion mode is changed from the diffusion combustion mode to the premixed combustion according to the operation region (the operation region mainly determined by the engine speed and the engine load, that is, the required total injection amount). Switch between two modes, mode.

  The diffusion combustion mode is a combustion mode in which a fuel-air mixture is ignited while fuel is injected near the compression top dead center (when the piston 4 is near the compression top dead center).

  The premix combustion mode is a combustion mode in which fuel and air are mixed in advance in the combustion chamber 9 (cylinder 2), and this mixture is ignited in the vicinity of the compression top dead center.

  In the premixed combustion mode, the combustion starts after the fuel and air are mixed in advance, so that the fuel can be burned efficiently, and the fuel efficiency can be improved and the generation of soot can be suppressed. However, in this premixed combustion mode, it is necessary to sufficiently mix fuel and air in a relatively short time until combustion starts, so that the injection amount is small, that is, the engine load is relatively low. This is only possible in a region where the engine speed is relatively low. Therefore, in the present embodiment, the low load low rotation speed region A1 where the engine speed is low and the engine load is small is set as the premixed combustion region where the premixed combustion mode is performed, and the remaining region A2 is set as the diffusion combustion mode. It is set to the diffusion combustion area to be implemented.

  Examples of the injection pattern for realizing each combustion mode and the heat generation rate in each combustion mode are shown in FIGS. 7 (a), 7 (b), and 7 (c). 7A and 7B show examples of the diffusion combustion mode, and FIG. 7C shows an example of the premixed combustion mode.

  As shown in FIG. 7A, in the diffusion combustion mode, the main fuel for generating the engine torque is injected in the vicinity of the compression top dead center, and the air-fuel mixture burns with the injection of this fuel.

  In the present embodiment, in the diffusion combustion region A2, in all regions except the high rotation high load region A2_c (see FIG. 6) where the engine speed is high and the engine load is high, the air utilization rate is improved and the main fuel is used. In order to improve the ignitability, the fuel is injected into the combustion chamber 9 before the main fuel injection. That is, in the present embodiment, in a specific region excluding the high rotation high load region A2_c in the diffusion combustion region A2, main injection (injecting fuel for generating engine torque in the vicinity of the compression top dead center into the combustion chamber 9) Main injection) Qm and pre-injection in which an amount of fuel smaller than the main injection is injected into the combustion chamber 9 at the timing before the main injection. Note that only the main injection is performed in the high rotation high load region A2_c. In the specific region, after the main injection Qm, after-injection that injects a smaller amount of fuel than the main injection Qm may be performed.

  Further, in the present embodiment, in the first region A2_a (see FIG. 6) in which the engine load is relatively low in the specific region, as shown in FIG. , Pre-injection Qpr). Specifically, pilot injection Qpi is performed relatively early, and then pre-injection Qpr is performed at a timing relatively close to the timing of main injection. With this injection pattern, the pilot injection Qpi, which is the first injection, can be performed to increase the premixability of fuel and air and increase the air utilization rate. The pilot injection Qpi and the pre-injection Qpr, which is the next injection, cause pre-combustion, which is combustion with a small amount of heat generation, immediately before the main-injected fuel Qm burns, that is, immediately before main combustion occurs. Thus, the main injected fuel can be easily burned. Further, in the above injection, the timing at which the pre-stage injection (pilot injection Qpi, pre-injection Qpr) is accommodated in the cavity 10, particularly, the mixture in which the equivalence ratio is locally 2.0 or more is generated in the combustion chamber 9. The local equivalent ratio in the combustion chamber 9 before the main combustion is increased.

  On the other hand, in the second region A2_b (see FIG. 6), the engine load is relatively high in the specific region, and if the pilot injection Qpi is performed, there is a risk that the fuel injected by the pilot injection Qpi may ignite early. As shown in b), only the pre-injection Qpr is performed at a timing relatively close to the timing of the main injection Qm.

  Here, in this embodiment, this pre-injection (pilot injection Qpi + pre-injection Qpr or pre-injection Qpr) is pre-injected as shown in the heat generation rate diagrams of FIGS. Combustion generated by the generated fuel (hereinafter sometimes referred to as pre-combustion) and combustion generated by the main-injected fuel (hereinafter also referred to as main combustion) occur in succession. A series of combustion is generated in the combustion chamber 9 by the injection.

  On the other hand, as shown in FIG. 7C, in the premixed combustion mode, fuel is injected into the combustion chamber 9 at a relatively early timing during the compression stroke, and the air-fuel mixture starts to combust after the end of the injection. Although FIG. 7C shows the case where fuel is injected in three times during the compression stroke, the number of injections is not limited to this.

  As described above, in the present embodiment, the combustion mode is switched according to the operation region, and the PCM 70 changes the injection pattern according to the operation region.

(3-3-2) Control Procedure of Injection System in Diffusion Combustion Mode Next, the control procedure of the injection system when the diffusion combustion mode is performed will be described with reference to FIG. Hereinafter, the control procedure of the injection system in the first region A2_a, that is, the control procedure of the injection system when performing the pilot injection Qpi and the pre-injection Qpr as the pre-stage injection will be described. The control procedure in the second region A2_b is a procedure described below (an injection system control procedure described in (3-3-2) and an injection timing correction procedure described in (3-3-3)). In FIG. 4, the pilot injection Qpr is omitted, and the pilot injection Qpi is replaced with the pre-injection Qpr.

  The PCM 70 functionally includes an injection control unit 71 that controls the injection system, and the injection control unit 71 controls the injection system.

  First, in step S1, the injection control unit 71 detects the injection pressure that is the detection value of the fuel pressure sensor SN6, the intake air temperature that is the detection value of the intake manifold temperature sensor SN3, and the intake air amount that is the detection value of the airflow sensor SN2 (fresh air amount). ), And reads the engine water temperature that is the detection value of the engine water temperature sensor SN5.

  Next, in step S2, based on the values read in step S1, etc., the state in the combustion chamber 9 (cylinder 2) after the intake valve 18 is closed and before fuel is injected (hereinafter referred to as cylinder) In some cases).

  In the present embodiment, as the in-cylinder state, the wall surface temperature of the combustion chamber 9, the in-cylinder temperature that is the temperature of the gas in the combustion chamber 9, the in-cylinder oxygen concentration that is the oxygen concentration of the gas in the combustion chamber 9, and the combustion chamber 9 The in-cylinder pressure that is the internal pressure is estimated.

  The wall surface temperature of the combustion chamber 9 is estimated from the engine water temperature, the engine speed, and the engine load. This estimation is performed, for example, by extracting a value from the map. The in-cylinder temperature is estimated from the intake air temperature, the EGR rate, and the like. The in-cylinder oxygen concentration is estimated from the intake air amount, the EGR rate, and the like. The in-cylinder pressure is estimated from the intake pressure and the engine speed at the closing timing of the intake valve.

  Next, in step S3, the injection control unit 71 determines the injection pressure, that is, the pressure accumulation chamber, based on the required total injection amount determined based on the target torque and the engine speed as described above and the engine speed. The target injection pressure which is the target value of the pressure (fuel pressure) of is determined. For example, the injection control unit 71 extracts a target injection pressure corresponding to the required total injection amount and the like from a map of the required total injection amount, the engine speed, and the target injection pressure that are preset and stored.

  In step S4, the injection control unit 71 determines the injection amount of the pre-injection Qpr based on the required total injection amount, the engine speed, and the in-cylinder state estimated in step S2. For example, the injection control unit 71 sets a value corresponding to the required total injection amount or the like from the map of the basic injection amount of the required total injection amount, the engine speed, and the pre-injection Qpr that is preset and stored. Extracted as injection quantity. Thereafter, the injection control unit 71 corrects the basic injection amount of the pre-injection Qpr according to the in-cylinder state. Specifically, correction is performed such that the lower the wall surface temperature of the combustion chamber 9, the lower the in-cylinder temperature, the lower the in-cylinder oxygen concentration, and the lower the in-cylinder pressure, the greater the injection amount of the pre-injection Qpr. . This is because the lower the wall temperature, in-cylinder temperature, in-cylinder oxygen concentration, and in-cylinder pressure of the combustion chamber 9, the lower the combustion efficiency of the fuel, and in order to ensure a predetermined amount of heat generated by the pre-injection Qpr, The pre-injection amount is corrected by these.

  Next, the injection control unit 71 determines the injection timing (injection start timing) of each injection based on the required total injection amount and the engine speed.

  Specifically, in step S5, the injection control unit 71 determines the injection timing of the main injection according to the required total injection amount and the engine speed. Further, an interval that is a period between the injection timings (injection start timings) of the respective injections (pilot, pre-main injection) is determined according to the required total injection amount and the engine speed.

  In step S6, the injection control unit 71 determines pilot injection and pre-injection injection timings based on the injection timing of the main injection and the interval.

  Next, in step S7, the injection control unit 71 determines the pilot injection amount. The procedure for determining the pilot injection amount will be described later.

  Next, in step S8, the injection control unit 71 performs main injection based on the required total injection amount, the injection amount of pre-injection determined in step S4, and the injection amount of pilot injection determined in step S7. Determine the injection quantity of Qm.

  After step S8, the process proceeds to step S9, where the injection control unit 71 controls the injector 20 so that the injection amount and the injection timing of each injection become the above determined values (commands the injector 20), and The fuel pressure regulator is controlled so that the injection pressure becomes the value determined in step S2.

(3-3-3) Procedure for Determining Pilot Injection Amount The procedure for determining the pilot injection amount in step S7 will be described with reference to FIG.

  In the present embodiment, as shown in FIG. 5, as a part for determining the pilot injection amount, the injection control unit 71 functionally includes a target pre-stage heat generation amount determination unit (target pre-stage heat generation amount determination means) 72, A spill amount calculation unit (spill amount calculation means) 73 and a pilot injection amount determination unit (previous injection amount determination means) 74 are included.

  The target pre-stage heat generation amount determination unit 72 sets the target value of the total heat generation amount generated by the pre-stage injection (pilot injection Qpi and pre-injection Qpr) necessary for making the combustion state of the main combustion appropriate and ensuring appropriate engine performance. Is calculated (step S11 in the flowchart of FIG. 9).

  In other words, the combustion state of the main injection, and hence the engine performance, changes depending on the heat generation amount of the front injection. Specifically, when the amount of heat generated by the pre-injection is excessively large, the temperature of the combustion chamber 9 at the time of main injection becomes higher, and thus the fuel injected by the main injection ignites earlier than the appropriate time. As a result, the amount of soot is increased. On the other hand, when the amount of heat generated by the front-stage injection is small, the temperature and pressure in the combustion chamber 9 cannot be sufficiently increased by the front-stage injection, causing problems such as deterioration of the ignitability of the main-injected fuel. On the other hand, the target pre-stage heat generation amount determination unit 72 determines the heat generation amount of the pre-injection (requested pre-stage heat generation amount) that can avoid the occurrence of the above problem. In the present embodiment, the required pre-stage heat generation amount is determined based on the required total injection amount and the engine speed. For example, a value is extracted from a map of the required total injection amount, the engine speed, and the required pre-stage heat generation amount that is preset and stored.

  The spill amount calculation unit 73 calculates a spill amount that is the amount of fuel that has not been stored in the cavity 10 and spilled outside the cavity 10 among the fuel amount (injection amount) injected in the previous stage (step S12).

  This will be specifically described with reference to FIG. FIG. 10 is a diagram showing a state in the combustion chamber 9 near the time when pilot injection is performed. As shown in FIG. 10, the pilot injection Qpi is at an earlier timing than the main injection performed near the compression top dead center, and the crown surface 4 a of the piston 4, the cavity 10, and the tip end portion 21 a of the injector 20. However, fuel is injected relatively far away. Therefore, a portion F1 of the injected fuel does not fit in the cavity 10 and is a portion outside the cavity 10 (radially outside the lip portion 13), that is, the diameter of the piston crown surface 12 is larger than that of the lip portion 13. It diffuses into a so-called squish area between the outer portion in the direction and the cylinder head 5. The spill amount is the amount of fuel diffused in the squish area, and the spill amount calculator 73 estimates and calculates this amount.

  Here, as the injection pressure of the pilot injection is higher and the reach of the fuel spray is longer, the amount of fuel that goes beyond the lip portion 13 toward the radially outer side, that is, the amount of spillage, increases. Further, as the injection timing of the pilot injection is earlier and the distance between the tip end portion 21a of the injector 20 and the crown surface 4a of the piston 4 is longer, the amount of spillage increases.

  Specifically, the relationship among the spill amount, the injection timing, and the injection pressure is as shown in FIG. FIG. 11 shows the relationship between different injection pressures with the horizontal axis representing the injection timing and the vertical axis representing the spillage. As shown in FIG. 11, when the injection timing is earlier than the predetermined timing, most of the injection amount exceeds the lip portion 13 and the spillage amount is almost constant, but the injection timing is later than this timing. On the corner side, the amount of spillage becomes smaller as the injection timing becomes later (closer to the compression top dead center). Moreover, the amount of spillage increases as the injection pressure decreases.

  Correspondingly, in this embodiment, the spill amount calculation unit 73 calculates the spill amount based on the injection pressure and the injection timing, and the injection pressure is high and the injection timing of the pilot injection is early (on the advance side). The amount of spillage is calculated so that the amount of spillage increases. For example, the spill amount calculation unit 73 stores a map similar to the graph shown in FIG. 11, and corresponds to the injection pressure detected in step S1 and the injection timing of pilot injection determined in step S6 from this map. Extract the value.

  The pilot injection amount determination unit 74 is a part that determines the injection amount of pilot injection based on the spill amount and the like. The pilot injection amount determination unit 74 functionally includes a combustion efficiency calculation unit (combustion efficiency calculation unit) 74a and a combustion efficiency correction unit (combustion efficiency correction unit) 74b.

  The combustion efficiency calculation unit 74a calculates the combustion efficiency of the pilot injection Qpi based on the calculated spill amount (step S13).

  As described above, the fuel spilled into the squish area is then further diffused in the squish area. For this reason, the equivalence ratio in the squish area is extremely small, and the fuel in the squish area hardly burns even by the subsequent compression of the piston. That is, the fuel spilled into the squish area does not burn at least before the start of main combustion and does not contribute to pre-combustion. Therefore, the greater the spill amount, the worse the combustion efficiency of the pilot injection Qpi.

  Correspondingly, in the present embodiment, the combustion efficiency calculation unit 74a calculates the combustion efficiency of the pilot injection Qpi so that the combustion efficiency decreases as the spill amount increases.

  Specifically, the relationship between the spill amount and the combustion efficiency is the relationship shown in FIG. FIG. 12 is a graph showing the result of a detailed investigation on the relationship between the spillage amount and the combustion efficiency, with the horizontal axis representing the spillage amount and the vertical axis representing the combustion efficiency. As shown in FIG. 12, the combustion efficiency basically deteriorates as the amount of spillage increases. However, when the amount of spillage is greater than or equal to the predetermined amount and below the predetermined amount, the amount of spillage may change. The combustion efficiency does not change much. In the present embodiment, the combustion efficiency calculation unit 74a calculates the combustion efficiency from the spill amount so that the relationship between the spill amount and the combustion efficiency becomes the relationship shown in FIG. For example, the combustion efficiency calculation unit 74a extracts the combustion efficiency corresponding to the amount of spillage from the stored map similar to the graph shown in FIG.

  The combustion efficiency correction unit 74b corrects the combustion efficiency of the pilot injection Qpi calculated by the combustion efficiency calculation unit 74a based on the amount of spillage according to the in-cylinder state (step S14). That is, the combustion efficiency varies depending on the in-cylinder state. Therefore, the combustion efficiency correction unit 74b corrects the combustion efficiency calculated by the combustion efficiency calculation unit 74a based on the in-cylinder state. Specifically, the combustion efficiency correction unit 74b has a lower combustion efficiency as the wall surface temperature of the combustion chamber 9 is lower, the in-cylinder temperature is lower, the in-cylinder oxygen concentration is lower, and the in-cylinder pressure is lower. Correct as follows.

  The pilot injection amount determination unit 74 determines the pilot injection amount based on each value determined and calculated as described above.

  Specifically, the pilot injection amount determination unit 74 calculates the heat generation amount of the pre-injection Qpr from the pre-injection amount determined in step S4, and the required pre-stage heat generation amount determined by the target pre-stage heat generation amount determination unit 72. From this, the heat value of the pre-injection Qpr is subtracted to calculate the target value of the heat value of the pilot injection Qpi (step S15). Thereafter, the pilot injection amount determination unit 74 calculates an injection amount that can achieve this target value based on the target value and the combustion efficiency of the pilot injection Qpi corrected by the combustion efficiency correction unit 74b. This calculated value is determined as the pilot injection amount (step S16).

  Thus, in the present embodiment, an appropriate pilot injection amount that satisfies the required pre-stage heat generation amount is determined in a state where the spill amount and the in-cylinder state are taken into account.

(4) Operation, etc. As described above, according to the present embodiment, a part of the injection amount of the front injection (pilot injection when pilot injection and pre-injection are performed, pre-injection when only pre-injection is performed) is The injection amount is determined in consideration of spilling out of the cavity 10 and at least not contributing to the main combustion. Therefore, it is possible to secure an appropriate amount of heat generated by the pre-injection and to make the combustion state of the main combustion and thus the engine performance more appropriate.

  In particular, in the present embodiment, the amount of spilling out of the cavity 10 in the preceding stage injection is estimated according to the injection pressure and the injection timing. Therefore, the amount of spillage can be estimated more accurately, and the injection amount and the heat generation amount of the pre-injection can be more appropriately made appropriate.

  More specifically, the spillage amount increases as the injection pressure increases and the distance that the fuel injected by the preceding stage reaches increases, and as the injection timing of the preceding stage is advanced and the distance between the injector and the cavity increases. Therefore, the amount of spillage can be appropriately estimated according to the injection pressure and the injection timing.

  Further, in the present embodiment, the combustion efficiency of the pre-stage injection is calculated based on the estimated spill amount, and the combustion efficiency is calculated in the cylinder state (the wall surface temperature of the combustion chamber 9, the cylinder temperature, the cylinder oxygen concentration, the cylinder interior Since the injection amount of the front injection is determined based on this combustion efficiency, in addition to the spill amount, a more appropriate injection amount of the front injection corresponding to the in-cylinder state, that is, the heat generation amount is realized. The combustion state of the main combustion and thus the engine performance can be made more appropriate.

(5) Modification Here, in the above-described embodiment, a case has been described in which only the pilot injection spill amount is estimated when pilot injection and pre-injection are performed. And the injection amount of the pre-injection may be determined based on the estimated value. That is, in the case of performing the pre-stage injection divided into a plurality of times, the spill amount may be estimated for each injection, and the injection amount of each injection may be determined based on this estimated value.

  However, when the pre-injection is performed in a plurality of times, the amount of spillage of the injection that is performed first and performed at the timing farthest from the compression top dead center becomes the largest. Therefore, if the amount of spillage is estimated only for this first injection and only the injection amount of the first injection is determined based on this estimated value, the heating value of the preceding injection can be made relatively simple. Can do.

  Moreover, the injection pattern of each driving | operation area | region is not restricted above. For example, in the diffusion combustion mode, further injection (so-called after injection or the like) may be performed after the main injection. Further, two or more injections may be performed as the pre-injection.

  The specific shape of the cavity 10 is not limited to the above.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder 71 Injection control part (injection control means)
72 Pre-target heat value determination unit (target pre-heat value determination means)
73 Spillage amount calculation unit (spillage amount calculation means)
74 Pilot injection amount determination unit (front injection amount determination means)
74a Combustion efficiency calculation unit (combustion efficiency calculation means)
74b Combustion efficiency correction unit (combustion efficiency correction means)

Claims (4)

In an engine fuel control device comprising an injection device capable of injecting fuel into a combustion chamber formed in a cylinder, and an injection control means for controlling the injection device,
A cavity that is recessed in a direction away from the bottom surface of the cylinder head is formed on the piston crown of the engine.
The injection control means includes
In at least a part of the operation region, the injection device performs the main injection and the front injection that injects an amount of fuel smaller than the injection amount of the main injection into the cylinder before the main injection,
A target pre-stage heat generation amount determining means for determining a target pre-stage heat generation amount that is a target value of a heat generation amount generated in the combustion chamber by burning the fuel injected in the previous stage based on operating conditions;
A spill amount calculating means for calculating a spill amount outside the cavity among the injection amounts of the preceding stage injection;
Pre-stage injection amount determination means for determining the injection amount of the pre-stage injection based on the calculated spill amount and the calculated target pre-stage heat generation amount,
An engine fuel control apparatus that causes the injection device to inject the injection amount determined by the preceding injection amount determination means when the front injection is performed. The fuel control apparatus for an engine according to claim 1,
The engine fuel control apparatus according to claim 1, wherein the spill amount calculation means calculates the spill amount as the injection pressure of the preceding injection is higher and the injection timing of the preceding injection is advanced. The engine fuel control device according to claim 1 or 2,
The preceding injection amount determining means is
Combustion efficiency calculating means for calculating the combustion efficiency of the fuel injected by the preceding injection based on the spill amount;
Combustion efficiency correction means for correcting the calculated combustion efficiency according to at least one of the wall surface temperature of the combustion chamber, the temperature of the gas in the combustion chamber, the oxygen concentration in the combustion chamber, and the pressure in the combustion chamber; Including
A fuel control apparatus for an engine, wherein an injection amount of the preceding injection is determined based on the corrected combustion efficiency and the target preceding injection heat generation amount. The engine fuel control apparatus according to any one of claims 1 to 3,
The injection control means performs the pre-stage injection divided into two or more times,
The target pre-stage heat generation amount determining means determines a target value of the heat generation amount generated in the combustion chamber by all pre-stage injections as the target pre-stage heat generation amount,
The spill amount calculating means calculates the spill amount of the first stage injection that is performed first,
The pre-stage injection amount determining means determines the injection amount of the pre-stage injection to be performed first based on the target pre-stage heat generation amount, the injection amount of the pre-stage injection after the second time, and the spill amount. The engine fuel control device.

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