JP2016070192A - Furl control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To favorably maintain the ignition performance of an air-fuel mixture in a cylinder when using a low-pressure EGR device.SOLUTION: In a fuel control device of an engine comprising a low-pressure EGR device 52 which connects a portion at a downstream side rather than an exhaust emission control device 41 and an intake passage 30, and recirculates exhaust emission, and a high-pressure EGR device 51 which connects a portion at an upstream side rather than the exhaust emission control device 41 and a portion at a downstream side rather than a connecting portion connected with the low-pressure EGR device 52 out of the intake passage 30, and recirculates the exhaust emission, the fuel control device identifies an oxygen concentration of a specified portion between the connecting portion of the low-pressure EGR device 52 and a connecting portion of the high-pressure EGR device 51 out of the intake passage 30, determines that a low-pressure EGR gas flows into the specified portion when the identified oxygen concentration is lowered to a prescribed value or lower, controls an injection amount of front-stage injection on the basis of a determination result, and increases the injection amount of front-stage injection when it is determined that the low-pressure EGR gas starts to flow into the specified portion.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an exhaust purification device, a low-pressure EGR device that connects a portion of the exhaust passage downstream of the exhaust purification device and the intake passage to recirculate exhaust gas to the intake passage, and an exhaust purification device of the exhaust passage. The present invention also relates to an engine fuel control device including a high-pressure EGR device that connects an upstream portion and a portion of an intake passage that is downstream of a connection portion with a low-pressure EGR device to recirculate exhaust gas to the intake passage.

  2. Description of the Related Art Conventionally, so-called EGR devices that recirculate exhaust gas exhausted from an engine to an intake passage have been used to improve engine performance such as exhaust performance.

  Further, as disclosed in Patent Document 1, for example, as the EGR device, a portion of the exhaust passage downstream of the exhaust purification device can be used so that the exhaust performance and the like can be controlled more finely and appropriately according to the operating conditions. And a low pressure EGR device that recirculates exhaust gas to the intake passage, and a portion of the exhaust passage that is upstream of the exhaust purification device and a portion of the intake passage that is downstream of the connection portion of the low pressure EGR device. It is known to provide a high-pressure EGR device that connects the parts to recirculate exhaust gas in the intake passage.

Japanese Patent No. 4380754

  Here, since the temperature of the exhaust gas in the portion downstream of the exhaust gas purification device in the exhaust passage is relatively low, when a part of this low temperature exhaust gas is recirculated to the intake passage using the low pressure EGR device, As a result of the temperature in the cylinder decreasing, the ignitability of the air-fuel mixture (fuel / air mixture) in the cylinder may deteriorate. In particular, at the start of exhaust gas recirculation by the low-pressure EGR device, low-temperature exhaust gas suddenly flows into the cylinder, so that the ignitability tends to be temporarily deteriorated.

  The present invention has been made in view of the above circumstances, and provides an engine fuel control device that can maintain good ignitability of an air-fuel mixture in a cylinder when a low-pressure EGR device is used. For the purpose.

  In order to solve the above problems, the present invention connects an exhaust purification device for purifying exhaust provided in an exhaust passage, and a portion of the exhaust passage downstream of the exhaust purification device and an intake passage. A low pressure EGR device that recirculates exhaust gas to the intake passage, a portion of the exhaust passage that is upstream of the exhaust purification device, and a portion of the intake passage that is downstream of the connection portion with the low pressure EGR device; And a high pressure EGR device that recirculates exhaust gas to the intake passage, and an injection device capable of injecting fuel into the engine cylinder, and an injection control means for controlling the injection device, A post-merging oxygen concentration specifying means for specifying an oxygen concentration in a specific portion between the connection portion of the low pressure EGR device and the connection portion of the high pressure EGR device in the intake passage, and the low pressure EGR device Low pressure EGR gas inflow state determining means for determining whether or not low pressure EGR gas that is exhaust gas recirculated to the intake passage flows into the specific portion. When the oxygen concentration specified by the combined oxygen concentration specifying means falls below a predetermined value, it is determined that the low-pressure EGR gas has flowed into the specified part, and the injection control means performs main injection in at least a part of the operation region. And the pre-stage injection in which the amount of fuel smaller than the injection amount of the main injection is injected into the cylinder prior to the main injection, and the determination result of the low-pressure EGR gas inflow state determination means Based on this, the injection amount of the pre-stage injection is controlled, and the low pressure EGR gas inflow state determination means starts the inflow of the low pressure EGR gas into the specific portion If it is determined that, to provide a fuel control system for an engine, characterized in that to increase the fuel injection amount of the preceding injection (claim 1).

  According to the present invention, the low-pressure EGR device can easily and accurately determine that the low-temperature low-pressure EGR gas has flowed into the intake passage and thus the cylinder, and based on this determination result, the injection amount of the pre-stage injection This injection amount can be made appropriate according to the inflow state of the low-pressure EGR gas. In particular, when it is determined that low-pressure EGR gas has flowed in, the injection amount of the front-stage injection is increased. Therefore, the temperature pressure in the cylinder before the main injection is increased, and the low-pressure low-pressure EGR gas flows in. The deterioration of the ignitability of the injected fuel can be suppressed, and the ignitability of the fuel can be maintained well.

  Specifically, the exhaust gas recirculated by the high pressure EGR device is not introduced into a portion of the intake passage downstream of the connection portion with the low pressure EGR device and upstream of the connection portion with the high pressure EGR device, Only the exhaust gas recirculated by the low pressure EGR device to the air flowing into the intake passage from the outside is introduced. Therefore, regardless of the driving state of the high pressure EGR device, if the exhaust gas recirculates from the low pressure EGR device, the oxygen concentration in this portion decreases. On the other hand, in the present invention, as described above, when the oxygen concentration in this portion is specified and the oxygen concentration falls below a predetermined value, the increase control of the injection amount is performed. Therefore, it is possible to easily and accurately estimate whether or not the low-temperature exhaust gas is introduced into the intake passage and hence into the cylinder by the low-pressure EGR device, and by controlling the injection amount of the pre-stage injection based on this estimation result, An appropriate amount of this injection amount can be secured to ensure the ignitability of the main injected fuel.

  In the present invention, the predetermined value is preferably set to 23%.

  As described above, in the portion of the intake passage that is downstream of the connection portion with the low-pressure EGR device and upstream of the connection portion with the high-pressure EGR device, the air flowing into the intake passage from the outside of the engine is introduced into the intake passage by the low-pressure EGR device. Refluxed exhaust is introduced. Therefore, if the oxygen concentration in this portion is equal to or lower than the oxygen concentration of air, it can be considered that the exhaust gas is recirculated. Therefore, if the predetermined value is set to 23% (weight%) which is the oxygen concentration of the air, it is estimated earlier that the exhaust gas is recirculated by the low pressure EGR device, and the main injection is performed more reliably. Fuel ignitability can be ensured.

  As the specific portion, for example, a portion in the vicinity of a throttle valve provided in a portion between the connection portion of the low pressure EGR device and the connection portion of the high pressure EGR device in the intake passage and capable of opening and closing the intake passage. (Claim 3).

  In the present invention, the exhaust gas is detected based on the fresh air amount detecting means for detecting the amount of fresh air flowing into the intake passage, the detected fresh air amount, and the injection amount injected from the injection device. An exhaust oxygen concentration calculating means for calculating an exhaust oxygen concentration that is an oxygen concentration in the passage; the specified exhaust oxygen concentration; and a time for the exhaust to move from a cylinder to a connection portion of the low pressure EGR device in the intake passage. The low pressure EGR side oxygen concentration calculating means for calculating the low pressure EGR side oxygen concentration which is the oxygen concentration of the gas flowing into the intake passage from the low pressure EGR device at the connection portion, and the intake passage by the low pressure EGR device. Low-pressure EGR gas flow rate calculating means for calculating a low-pressure EGR gas flow rate that is the amount of gas recirculated to the exhaust gas, and the post-merging oxygen concentration specifying means is configured to detect the fresh air amount detected Based on the specified low-pressure EGR side oxygen concentration and the calculated low-pressure EGR gas flow rate, the oxygen concentration of the mixture of the low-pressure EGR gas and fresh air at the connection portion is calculated, and the calculated mixture It is preferable to calculate the oxygen concentration of the specific portion based on the oxygen concentration of the gas.

  In this way, since the oxygen concentration of the gas passing through the specific portion can be specified without providing a sensor for detecting the oxygen concentration, the structure can be simplified and advantageous in terms of cost. It becomes.

  In the present invention, an intake air temperature estimating means for estimating the temperature of gas passing through a portion downstream of the connection portion with the high pressure EGR device in the intake air passage is provided, and the injection control means cools the engine. When the engine water temperature, which is the temperature of the cooling water to be performed, is equal to or lower than a preset reference temperature, the injection amount of the pre-stage injection is controlled based on the determination result of the low pressure EGR gas inflow state determination means, while the engine water temperature Is higher than the reference temperature, it is preferable to control the injection amount of the pre-stage injection based on the temperature estimated by the intake air temperature estimation means regardless of the determination result (Claim 5).

  In this case, the engine water temperature is high, and accordingly, the temperature of the exhaust gas introduced into the cylinder by the low pressure EGR device is relatively high, and the difference from the temperature of the exhaust gas introduced into the cylinder by the high pressure EGR device is reduced. When it is relatively easy to estimate the temperature of these mixed gases and thus the gas introduced into the cylinder, the ignition quality of the main injected fuel is determined by determining the injection amount of the pre-stage injection based on the estimated temperature. When the temperature of the engine water is low and the temperature difference is large, and accordingly, it is difficult to estimate the temperature of the gas introduced into the cylinder, the oxygen concentration of the specific portion is as described above. Accordingly, the ignitability can be ensured by determining the injection amount of the pre-stage injection, and this ignitability can be ensured more reliably regardless of the engine water temperature.

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 mode switching area | region. (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. (C) 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 figure which showed the mode of pilot injection. It is the flowchart which showed the flow of the whole control procedure of the injection system. It is the graph which compared the estimated value of ignition delay, and the measured value. It is the flowchart which showed the flow of the pilot injection amount determination procedure. It is the flowchart which showed the calculation procedure of the throttle part oxygen concentration.

(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. Cooling water for cooling the engine is introduced into the intercooler 35, and air is cooled by this cooling water.

  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 EGR device (hereinafter referred to as HP_EGR device) 51, a low-pressure 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. Thus, the exhaust gas (low pressure EGR gas) recirculated by the LP_EGR device 52 is exhaust gas that has passed through the turbine 62 and further the DPF 41b, and its temperature and pressure are relatively low. Furthermore, in the present embodiment, as described above, the low-pressure EGR gas is cooled by the EGR cooler 52c, and the temperature of the low-pressure ER gas is lowered when it flows into the intake passage 30.

(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 a fuel injection valve 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 (cylinder 2) and an exhaust gas generated in the combustion chamber 9 to the exhaust passage 40. The exhaust port 17, the intake valve 18 that opens and closes the opening of the intake port 16 on the combustion chamber 9 side, and the exhaust valve 19 that opens and closes the opening of the exhaust port 17 on the combustion chamber 9 side 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. 3 and 4, the symbol F indicates the spray of fuel injected from the injection hole 22 of 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 bores 22 are formed at the tip end portion 21a is used. The respective fistulas 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 of the cavity 10, and is formed so that the top of the raised portion is located directly below the distal end portion 21 a of the fuel injection valve 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 15. 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 15. Based on the pulse signal, the rotation angle and the rotation speed of the crankshaft 15 are output. That is, the engine speed is specified.

  An air flow sensor SN2 (new air amount detection means) that detects the amount of air that passes through the air cleaner 31 and is sucked into each cylinder 2 is located near the air cleaner 31 in the intake passage 30 (the portion between the air cleaner 31 and the compressor 61). ) Is provided.

  An intake pressure sensor SN3 for detecting the air passing through this portion and the pressure of the intake air taken into the cylinder 2 is provided in a portion of the intake passage 30 downstream of the intercooler 35.

  The surge tank 37 is provided with an intake manifold temperature sensor SN4 that detects the temperature of the gas in the surge tank 37, that is, the gas sucked into each cylinder 2.

  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 linear O2 sensor SN6 that detects the oxygen concentration in the exhaust gas is provided in a portion of the exhaust passage 40 downstream of the connection portion of the LP_EGR passage 52a.

  A fuel pressure sensor SN <b> 7 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.

  The exhaust passage 40 is provided with a differential pressure sensor SN8 that detects a differential pressure before and after (upstream and downstream ends) of the DPF 41b.

  Further, the vehicle is provided with an accelerator opening sensor SN9 for detecting the opening degree of an accelerator pedal (accelerator opening degree) operated by the driver, 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 fuel pressure regulator, the throttle valve 36, 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 SN9), and is specified by the target torque and the engine speed (detected value of the crank angle sensor SN1). The required total injection amount which is a basic value of the total amount of fuel injected into the combustion chamber 9 (cylinder 2) is determined based on the above. For example, the PCM 70 extracts a value corresponding to the accelerator opening from a map of the accelerator opening and the target torque set in advance and stored, and a map of the target torque, the engine speed and the required total injection amount. By doing so, the above values are determined.

  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.

  Here, in the present embodiment, the EGR control mode is switched as shown in FIG. Specifically, only the HP_EGR 51 that recirculates high-temperature EGR gas is performed in the low-rotation low-load region B1 where the required total injection amount (engine load) and the engine speed are low and the temperature in the cylinder 2 is relatively low. Total injection amount (in the high rotation and high load region B3 where the engine load and the engine speed are high and the temperature in the cylinder 2 is relatively high, only LP_EGR51 for recirculating low temperature EGR gas is performed, and an intermediate region therebetween In B2, both HP_EGR51 and LP_EGR51 are performed, and the ratio of LP_EGR51 is increased as the load is higher or the engine speed is higher.

(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.

  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. 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.

  In step S1, the injection control unit 71 determines the injection pressure, that is, the pressure in the pressure accumulating 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. A target injection pressure that is a target value 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 S2, the injection control unit 71 determines the injection amount of the pre-injection Qpr based on the required total injection amount and the engine speed. 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 required total injection amount, the engine speed, and the injection amount of the pre-injection Qpr that is preset and stored. Extract as

  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 S3, 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 S4, the injection control unit 71 determines the injection timing of pilot injection and pre-injection based on the injection timing of main injection and this interval.

  Next, in step S5, 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 S6, the injection control unit 71 performs main injection based on the required total injection amount, the injection amount of the pre-injection determined in step S4, and the injection amount of the pilot injection determined in step S7. Determine the injection quantity of Qm.

  After step S6, the process proceeds to step S7, and 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) Determination procedure of pilot injection amount The determination procedure of the pilot injection amount in step S5 will be described.

  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 first pilot injection amount determination unit 72 and a second pilot injection amount determination unit. 73.

  The first pilot injection amount determination unit 72 is a part that determines the pilot injection amount when the engine water temperature is equal to or lower than a reference temperature (for example, 70 ° C.). On the other hand, the second pilot injection amount determination unit 73 is a part that determines the pilot injection amount when the engine water temperature is higher than the reference temperature.

(I) Determination Procedure of Second Pilot Injection Amount Determination Unit 73 The second pilot injection amount determination unit 73 determines whether or not the main combustion ignition delay (from the injection start timing of the main injection until the main combustion starts, that is, the main injected fuel is The time until combustion starts) is estimated, and the pilot injection amount is determined so that this ignition delay becomes the target value.

  Specifically, the second pilot injection amount determination unit 73 first estimates the ignition delay of the main combustion. In this embodiment, this ignition delay τ_m is calculated by the following equation (1).

τ_m = A × P _TDC ^B × exp (1 / T _TDC ) ^C × NE ^D × CCLD ^E (1)
In Equation (1), P _TDC is the pressure in the combustion chamber 9 (cylinder 2) at the time of non-combustion at the compression top dead center, T _TDC is the temperature in the combustion chamber 9 at the time of non-combustion at the compression top dead center, NE is the engine speed, and CCLD is the oxygen concentration in the combustion chamber 9 (oxygen concentration before combustion). A, B, C, D, and E are constants. Among these constants, A, C, and D are positive values, B and E are negative values, and the pressure, temperature, and oxygen concentration are The higher the engine speed is, the shorter the ignition delay is.

  The above formula (1) is a simplification of the so-called Arrhenius empirical formula shown by the following formula (2), and is adapted to the diffusion combustion mode in the present embodiment.

τ = K1 × φ ^K2 × P ^K3 × exp (K4 / T) (2)
In this equation (2), φ is the equivalence ratio of the air-fuel mixture immediately before the fuel ignites, P is the atmospheric pressure (pressure in the combustion chamber) immediately before the fuel ignites, specifically oxygen in the combustion chamber T is the ambient temperature (temperature in the combustion chamber) just before the fuel is ignited, and K1 to K4 are constants.

  Here, in the equation (1), the term of the equivalence ratio φ in the equation (2) is included in the constant A. In diffusion combustion, the inventors of the present invention have found out as a result of intensive studies, when an air-fuel mixture having a relatively high equivalence ratio is generated at least locally in the combustion chamber before the main combustion by performing the pre-stage injection. Based on the finding that the ignition delay of main combustion does not change much with the equivalence ratio. That is, in the present embodiment, in the diffusion combustion mode, since the air-fuel mixture having a relatively large equivalence ratio can be generated at least locally in the combustion chamber before the main combustion by performing the pre-stage injection, the equivalence ratio φ is used as a variable. The ignition delay can be accurately calculated without using it.

  FIG. 10 shows a result of comparing the ignition delay estimated using the above formula (1) with the actually measured ignition delay under various operating conditions. In FIG. 10, the horizontal axis represents the actual measured value of the ignition delay, and the vertical axis represents the estimated value of the ignition delay calculated using the above equation (1). As apparent from FIG. 10, the estimated value of the ignition delay calculated by the equation (1) and the actually measured value almost coincide with each other, and the ignition delay is accurately calculated by the equation (1). In FIG. 10, as the ignition delay, instead of the time from the injection start time to the start of combustion, the time from the injection start time to the time when the heat generation rate peaks has a high correlation with this time.

The compression top dead center pressure P _TDC at the time of non-combustion in the formula (1) takes into account the cooling loss and the constant value of PV ^κ, when the detected value of the intake manifold pressure sensor SN3 and the intake valve 18 are closed This is calculated by fitting the volume of the combustion chamber of the combustion chamber and the volume of the combustion chamber at the compression top dead center. The specific heat ratio κ is set based on the gas component before injection in the combustion chamber specified based on the EGR rate and the like.

  The cooling loss is calculated based on the estimated values of the engine speed, the engine water temperature, and the temperature of the gas flowing into the cylinder 2 (intake air temperature). For example, the second pilot injection amount determination unit 73 determines a cooling loss by extracting a value corresponding to the engine speed and the like from a map of the engine speed and the cooling loss that is preset and stored.

  Here, as described above, in the present embodiment, the surge tank 37 is provided with the intake manifold temperature sensor SN4 for detecting the temperature. However, the temperature sensor is not sufficiently responsive. Therefore, in this embodiment, the intake air temperature is estimated. In other words, the PCM 70 is functionally provided with an intake air temperature estimation unit (intake air temperature estimation means) for estimating the intake air temperature, and using the intake air temperature estimated by the intake air temperature estimation unit, a cooling loss, As a result, the ignition delay is estimated. In the present embodiment, the intake air temperature is estimated in this way, but the estimated accuracy is improved by appropriately correcting this estimated value by the detected value of the intake manifold temperature sensor SN4.

  In the present embodiment, the intake air temperature estimation unit includes the high pressure EGR gas amount (estimated based on the engine speed and engine load, the opening degree of the HP_EGR valve 51b, etc.) and the low pressure EGR gas amount (engine speed and engine load and LP_EGR. The intake air temperature is estimated based on the fresh air amount (detected value of the airflow sensor SN2) and the like.

The compression top dead center temperature T _TDC at the time of non-combustion is calculated by applying the calculated compression top dead center pressure P _TDC at the time of non-combustion to the state equation of gas.

  The oxygen concentration CCLD in the combustion chamber is determined by the detection value of the linear O2 sensor SN6, that is, the oxygen concentration in the exhaust gas, the detection value of the intake air sensor SN2, that is, the amount of fresh air (air) sucked into the cylinder 2, and the EGR rate. Calculated based on

  In addition, as a result of various experiments, the present inventors have found that, in actual engine operation, ignition delay with the compression top dead center temperature and pressure as the representative temperatures without considering the temperature and pressure time history as described above. As a result, it has been found that the ignition delay is estimated to be shorter than the actual value as the engine speed increases. This is presumably because the higher the engine speed, the greater the change in crank angle per unit time and the higher the rate of increase in temperature and pressure per hour. Therefore, in the present embodiment, as described above, the ignition delay is estimated in consideration of the engine rotational speed, so that the compression top dead center temperature and pressure are set as the representative temperature and pressure without considering the temperature history and pressure history. Increase the accuracy of ignition delay while using.

  In the present embodiment, the constants A, B, C, D, and E are constant values regardless of the operation region. The values of these constants vary depending on the engine (combustion chamber shape, injector nozzle hole shape, etc.). Therefore, these constants may be set as appropriate for each engine.

  These constants change to some extent depending on the EGR rate, but it is known that when the EGR rate changes within a predetermined range, they may be the same value. In the present embodiment, the change in the EGR rate is within a predetermined range in the first region A2_a and the second region A2_b. Therefore, in the present embodiment, as described above, the ignition delay is calculated with these constants being constant.

  After calculating the ignition delay τ_m as described above, the second pilot injection amount determining unit 73 obtains a difference between the ignition delay τ_m and a preset target value of the ignition delay τ_m, and according to this difference. A preset basic value of the pilot injection amount is corrected.

  Specifically, the second pilot injection amount determination unit 73 determines the target value of the ignition delay τ_m and the basic value of the pilot injection amount based on the required total injection amount and the engine speed. Then, when the estimated value of the ignition delay τ_m is shorter than the target value of the ignition delay τ_m, in order to lengthen the ignition delay, the amount of heat generated by the pre-combustion is suppressed to thereby reduce the ambient temperature pressure before the main combustion. In order to decrease the final pilot injection amount, the final pilot injection amount is made smaller than the basic value. On the other hand, when the estimated value of the ignition delay τ_m is longer than the target value of the ignition delay τ_m, in order to shorten the ignition delay, the amount of heat generated by the pre-combustion is increased and the ambient temperature pressure before the main combustion is increased. In order to achieve this, the final pilot injection amount is made larger than the basic value.

  According to the procedure of the second pilot injection amount determining unit 73 described above, the ignition delay of the main combustion is made appropriate, the timing at which the main combustion occurs, the speed of the main combustion (rising rate of the heat generation rate), etc. are made appropriate, Engine performance such as engine torque, combustion noise, and soot generation can be improved.

  However, when the engine water temperature is low, it is difficult to accurately estimate the intake air temperature and thus the ignition delay, and there is a possibility that the engine performance cannot be secured by the control based on the ignition delay.

  Specifically, in a state where the engine water temperature is low and the engine body and the exhaust passage 40 are not sufficiently warmed, the temperature of the low pressure EGR gas returning to the intake passage 30 on the downstream side of the exhaust passage 40 becomes low, and the high pressure EGR The temperature difference from the gas will increase. In particular, in the present embodiment, the low pressure EGR gas flows into the cylinder 2 after passing through the intercooler 35 into which engine cooling water is introduced. Therefore, the temperature difference becomes larger under operating conditions where the engine water temperature is low. . Therefore, in order to accurately estimate the intake air temperature in this state, it is necessary to accurately estimate the ratio of the high pressure EGR gas and the low pressure EGR gas flowing into the cylinder 2. However, it is difficult to estimate this ratio, that is, the degree of mixing of the high pressure EGR gas and the low pressure EGR gas, and the intake air temperature cannot be accurately estimated.

  Therefore, in the present embodiment, when the engine water temperature is low, the pilot injection amount is determined by the second pilot injection amount determination unit 73 in a procedure different from the procedure by the first pilot injection amount determination unit 71.

  Here, as described above, the temperature of the low-pressure EGR gas is relatively low. In particular, when the engine water temperature is low, this temperature becomes lower. Therefore, when the low-pressure EGR gas flows into the cylinder 2, the temperature in the cylinder 2 decreases and the ignitability of the main combustion deteriorates. Therefore, when the low pressure EGR gas flows into the cylinder 2, the injection amount of the pilot injection is increased to increase the amount of pilot injection compared to the case where the low pressure EGR gas does not flow into the cylinder 2 in order to ignite the main combustion more appropriately. It is necessary to increase the temperature pressure before combustion.

  From this point of view, the second pilot injection amount determination unit 73 determines the injection amount of the pilot injection, and switches the injection amount of the pilot injection depending on whether or not the low pressure EGR gas is flowing into the cylinder 2. . Details of the procedure for determining the injection amount of the pilot injection by the second pilot injection amount determination unit 73 will be described next.

(Ii) Determination procedure of first pilot injection amount determination unit 71 The PCM 70 functionally includes an exhaust oxygen concentration calculation unit (exhaust oxygen concentration calculation means) 74a and a low pressure EGR side oxygen concentration calculation unit (low pressure EGR side oxygen concentration calculation). Means) 74b, a low pressure EGR gas flow rate calculation unit (low pressure EGR gas flow rate calculation unit) 74c, a post-merging oxygen concentration calculation unit (post-merge oxygen concentration specifying unit) 74d, and a low pressure EGR gas inflow state determination unit (low pressure EGR gas). Inflow state determination means) 74e.

  The exhaust oxygen concentration calculation unit 74a is a portion that specifies the oxygen concentration in the exhaust passage 40 and the exhaust oxygen concentration (wt%) that is the oxygen concentration of the exhaust discharged from the cylinder 2. The exhaust oxygen concentration calculation unit 74a calculates the exhaust oxygen concentration based on the fresh air amount detected by the air flow sensor SN2 and the injection amount injected from the injector 20. In the present embodiment, simply, assuming that a predetermined proportion of the injection amount reacts with oxygen, the remaining oxygen amount obtained by subtracting the reacted oxygen amount from the oxygen amount in the gas in the cylinder is replaced by the gas amount. The calculated value is calculated as the exhaust oxygen concentration.

  The low pressure EGR side oxygen concentration calculation unit 74b is connected to the intake passage 20 from the low pressure EGR passage 52a in a connection portion (hereinafter, also referred to as a low pressure side connection portion) 52d (see FIG. 1) between the intake passage 30 and the low pressure EGR passage 52a. This is a portion for specifying the low pressure EGR side oxygen concentration which is the oxygen concentration of the gas flowing into the gas. The low pressure EGR side oxygen concentration calculation unit 74b is based on the exhaust oxygen concentration calculated by the exhaust oxygen concentration specifying unit 74a and the time during which the exhaust moves from the cylinder 2 to the low pressure side connection unit 52d, that is, the transport delay time. Specify the side oxygen concentration. Specifically, the low pressure EGR side oxygen concentration calculation unit 74b calculates the transportation delay time based on the path length from the cylinder 2 to the low pressure side connection unit 52d and the engine speed, and before this transportation delay time, Is determined as the current low-pressure EGR-side oxygen concentration.

  The low pressure EGR gas flow rate calculation unit 74c is a part that calculates the low pressure EGR gas flow rate (the amount of gas that passes through the low pressure EGR passage 52b and is recirculated to the intake passage 30). The low pressure EGR gas flow rate calculation unit 74c calculates the flow rate based on the difference between the pressure at the inlet (connection portion with the exhaust passage 40) of the low pressure EGR passage 52b and the pressure at the outlet (connection portion with the intake passage 30). calculate. The pressure at the inlet of the low pressure EGR passage 52b is specified based on the detection value of the differential pressure sensor SN9. Further, the pressure at the outlet of the low pressure EGR passage 52b is extracted from a preset map of these and pressure in accordance with the engine speed and the engine load.

  The post-merging oxygen concentration calculation unit 74d is an oxygen concentration in the vicinity (specific portion) of the throttle valve 36 located between the low pressure side connection portion 52d and the connection portion 51d (see FIG. 1) of the high pressure EGR passage 51a in the intake passage 30. This is a part that specifies (% by weight). In this embodiment, the oxygen concentration in the portion immediately upstream of the throttle valve 36 (hereinafter, this oxygen concentration may be referred to as the throttle portion oxygen concentration) is specified.

  The post-merging oxygen concentration calculation unit 74d first performs the fresh air amount detected by the airflow sensor SN2, the low pressure EGR side oxygen concentration calculated by the low pressure EGR side oxygen concentration calculation unit 74b, and the low pressure EGR gas flow rate calculation unit 74c. Based on the calculated low pressure EGR gas flow rate, the oxygen concentration of the low pressure side connecting portion 52d is calculated. Then, the oxygen concentration of the throttle valve portion is calculated based on the oxygen concentration of the low pressure side connection portion 52d and the time during which the gas moves from the low pressure side connection portion 52d to the vicinity of the throttle valve 36, that is, the transport delay time.

  In other words, the post-merging oxygen concentration calculation unit 74d determines the oxygen concentration of the air-fuel mixture that is generated by mixing the air with the oxygen concentration of 23% and the low-pressure EGR gas with the low-pressure EGR side oxygen concentration by the fresh air amount and the low-pressure EGR gas flow rate, respectively. Is calculated based on these values. The oxygen concentration after the gas having this oxygen concentration has moved from the low-pressure side connecting portion 52d to the vicinity of the throttle valve 36 is set as the current throttle portion oxygen concentration. Specifically, the post-merging oxygen concentration calculation unit 74d calculates the transport delay time based on the path length from the low pressure side connection unit 52d to the throttle valve 36 and the engine speed, and before this transport delay time, The oxygen concentration of the low-pressure side connection portion 52d is specified as the current throttle portion oxygen concentration.

  The low pressure EGR gas inflow state determination unit 74e is a part for determining whether or not the low pressure EGR gas has flowed into the vicinity of the throttle valve 36. The low pressure EGR gas is exhaust gas after combustion, and the oxygen concentration thereof is lower than the oxygen concentration of air. Therefore, in the present embodiment, the low pressure EGR gas inflow state determination unit 74e causes the low pressure EGR gas to flow into the vicinity of the throttle valve 36 when the specified throttle portion oxygen concentration is 23% by weight or less which is the oxygen concentration of air. It is determined that On the other hand, the low pressure EGR gas inflow state determination unit 74e indicates that the low pressure EGR gas does not flow in the vicinity of the throttle valve 36 when the specified throttle portion oxygen concentration is higher than 23% that is the oxygen concentration of air. Is determined.

  As described above, in this embodiment, the inflow state of the low pressure EGR gas is determined in the vicinity of the throttle valve 36.

  The first pilot injection amount determining unit 72 switches the injection amount of the pilot injection between using and not using the low pressure EGR according to the determination result. That is, when it is determined that the low pressure EGR gas is flowing in the vicinity of the throttle valve 36, the first pilot injection amount determination unit 71 sets the injection amount of the pilot injection in advance for the presence of the low pressure EGR gas. When it is determined that the low-pressure EGR gas is not flowing, the injection amount of the pilot injection is set to a value set in advance for the absence of the low-pressure EGR gas. In the present embodiment, the first pilot injection amount determining unit 71 stores a map of preset pilot injection amounts for the presence and absence of low pressure EGR gas, and the first pilot injection amount determining unit 71. Switches the map for extracting the injection amount according to each case. These maps are, for example, maps of engine speed, engine load, and injection amount, and the first pilot injection amount determination unit 72 extracts values according to the engine speed and engine load.

  Here, as described above, when the low pressure EGR gas flows into the cylinder 2, the injection of pilot injection is performed more than when the low pressure EGR gas does not flow into the cylinder 2 in order to ignite the main combustion more appropriately. It is necessary to increase the amount to increase the temperature pressure before main combustion. On the other hand, the map is set so that the injection amount of pilot injection is larger in the same operating conditions (engine speed and engine load) than in the case of low pressure EGR gas. Yes. Therefore, at least under the same operating conditions, the amount of pilot injection is increased when it is determined that low-pressure EGR gas is flowing. Further, if it is determined that the low pressure EGR gas has flowed from the state where it is determined that the low pressure EGR gas does not flow into the cylinder 2 under the predetermined operating condition, the injection amount of the pilot injection is increased.

  In the present embodiment, the switching of the pilot injection amount is performed after a predetermined number of cycles have elapsed since the determination result has changed. In other words, the above determination is made as to whether or not the low pressure EGR gas is flowing in the vicinity of the throttle valve 36. The low pressure EGR gas existing in the vicinity of the throttle valve 36 is predetermined until the cylinder 2 is reached. The cycle passes. Therefore, in this embodiment, the injection amount of the pilot injection is switched after a predetermined number of cycles after the determination result changes. In other words, the injection amount of the pilot injection is switched based on the determination result before the predetermined number of cycles. The predetermined number of cycles is determined by the time required for the gas to move from the throttle valve 36 to the cylinder 2 and is determined based on the path length from the throttle valve 36 to the cylinder 2 in the intake passage 30 and the engine speed.

(Iii) Overall Flow of Pilot Injection Amount Determination Procedure The procedure for determining the pilot injection amount described above can be briefly summarized as shown in FIG.

  First, in step S11, it is determined whether or not the engine water temperature is equal to or lower than a reference temperature.

  If the determination in step S11 is yes, the process proceeds to step S12. In step S12, the ignition delay is estimated, and the pilot injection amount is determined based on this ignition delay.

  On the other hand, if the determination in step S12 is no, the process proceeds to step S13. In step S13, the throttle portion oxygen concentration is estimated.

  The throttle portion oxygen concentration is estimated according to the procedure shown in FIG. Specifically, in step S21, the exhaust oxygen concentration is estimated based on the total injection amount and the fresh air amount. Next, in step S22, the oxygen concentration at the outlet of the LP_EGR passage 52a is estimated based on the exhaust oxygen concentration estimated in consideration of the transport delay. Next, in step S23, the low-pressure EGR gas flow rate is estimated. Next, in step S24, the oxygen concentration of the low-pressure side connection 52d is estimated based on the oxygen concentration at the LP_EGR passage outlet, the low-pressure EGR gas flow rate, and the fresh air amount. Thereafter, in step S25, the throttle portion oxygen concentration is estimated based on the estimated oxygen concentration of the low pressure side connection portion 52d in consideration of the transport delay.

  After the throttle portion oxygen concentration is thus estimated, the process returns to step S14 in FIG. 11 to determine whether or not the throttle portion oxygen concentration before the predetermined number of cycles is 23% or less.

  If the determination in step S14 is no, the process proceeds to step S15. In step S15, assuming that the low pressure EGR gas does not flow into the cylinder 2, the pilot injection amount is determined from the map for no LP_EGR.

  On the other hand, if the determination in step S14 is yes, the process proceeds to step S16. In step S16, assuming that the low pressure EGR gas is flowing into the cylinder 2, the pilot injection amount is determined from the map for LP_EGR.

(4) Operation and the like As described above, according to the present embodiment, the slot portion oxygen concentration, that is, the downstream side of the connection portion 52d of the low pressure EGR device in the intake passage 30 and the connection portion 51d of the high pressure EGR device. Also, the oxygen concentration in the upstream portion is estimated, and the oxygen concentration in the portion where only the low pressure EGR gas is mixed with the fresh air is estimated, and whether or not this oxygen concentration has dropped to 23% or less, which is the fresh air oxygen concentration. Therefore, it is determined whether or not the low-pressure EGR gas has flowed into the intake passage 30 and thus the cylinder 2. This determination can be made more easily and accurately.

  Specifically, the oxygen concentration in the portion of the intake passage 30 downstream of the connection portion 51d of the low pressure EGR device includes the high pressure EGR gas in addition to the low pressure EGR gas in the intake air. It is difficult to determine whether or not it has been done. Further, it may be possible to determine whether or not the low pressure EGR gas has flowed in accordance with the opening degree of the LP_EGR valve 52b. However, since this valve has a response delay, the determination accuracy based on the opening degree of the valve is not sufficient. Is difficult to sufficiently increase. On the other hand, according to the procedure of this embodiment, the inflow state of the low-pressure EGR gas can be determined easily and reliably.

  According to the present embodiment, the injection amount of pilot injection (pre-stage injection) is switched between using and not using low-pressure EGR gas based on the determination result, and the injection amount of pilot injection according to the presence or absence As a result, the ignitability and combustion state of the main injection can be made appropriate, and good engine performance can be ensured. In particular, in the case of low pressure EGR gas under the same operating conditions (engine speed and engine load), the injection amount of pilot injection is set to be larger, so that low pressure EGR gas does not flow in the cylinder 2 When the low pressure EGR gas flows in from a state where the temperature of the engine is maintained at a relatively high level, and the temperature in the cylinder rapidly decreases as the low pressure EGR gas flows in, the pilot injection amount is increased. Therefore, it is possible to increase the ambient temperature pressure before the main injection, and to suppress the deterioration of the ignitability of the main combustion due to the decrease in the temperature (the temperature before the start of compression), and to ensure proper combustion and thus engine performance. it can.

  In this embodiment, since the inflow state of the low pressure EGR gas is determined based on whether or not the oxygen concentration has decreased to 23% or less, which is the fresh air oxygen concentration, the low pressure EGR gas flows into the intake passage 30 side. This can be identified earlier, and the ignitability and combustion state of the main injection can be made more appropriate.

(5) Modified Example Here, in the above embodiment, when it is determined that the low-pressure EGR gas has flowed into the vicinity of the throttle valve 36 when the oxygen concentration (wt%) of the throttle section is 23 wt% or less, which is the oxygen concentration of air. However, this determination value is not limited to 23% by weight. For example, when the inflow amount of the low pressure EGR gas is small, the value may be lower than 23 when the influence of the inflow of the low pressure EGR gas is considered to be small.

  In the above embodiment, the case where the post-merging oxygen concentration calculation unit 74d estimates the oxygen concentration in the vicinity of the throttle valve 36 has been described. However, the estimation portion includes the low pressure side connection portion 52d and the high pressure side connection portion 51d. If it is a part between, it will not be restricted to this. However, depending on the opening degree of the throttle valve 36, the gas flow rate may change between the upstream side and the downstream side of the throttle valve 36 and the transport delay amount may be different. Therefore, the oxygen concentration in the vicinity of the throttle valve 36 is estimated. preferable.

  Moreover, although the said embodiment demonstrated the case where the injection quantity of pilot injection (pre-stage injection) was switched after a predetermined cycle after the throttle part oxygen concentration fell to 23% or less, switching may be performed at the time of reduction. . That is, the pilot injection amount may be increased when the throttle portion oxygen concentration is reduced to 23% or less. In this case, even if there is an error or variation in the transport delay between the vicinity of the throttle valve 36 and the cylinder 2, the deterioration of the main combustion accompanying the inflow of the low-pressure EGR gas into the cylinder 2 is more reliably ensured. Can be avoided.

  In the above embodiment, when the engine water temperature is equal to or higher than the reference temperature, the second pilot injection amount determination unit 73 has described the case where the injection amount of the pilot injection is determined based on the estimated value of the ignition delay. Even when the engine water temperature is equal to or higher than the reference temperature, the first pilot injection amount determination unit 72 may be configured to control the injection amount of pilot injection according to the throttle portion oxygen concentration. Further, when the engine water temperature is equal to or higher than the reference temperature, the injection amount of pilot injection may be controlled based on an index other than the ignition delay. However, if the engine water temperature is equal to or higher than the reference temperature, the ignition delay can be accurately estimated. Therefore, if the injection amount is controlled by this ignition delay, the combustion state of the main combustion can be made more direct. it can.

  Moreover, the injection amount of the pilot injection may be switched based on the throttle portion oxygen concentration only in the region where the EGR control mode (whether the LP_EGR 51 is operated or the HP_EGR 52 is operated) is switched.

  In the above embodiment, the case where the throttle portion oxygen concentration (the oxygen concentration in the vicinity of the throttle valve 36) is specified is described. However, the throttle portion oxygen concentration may be specified using an oxygen concentration sensor. . However, if the throttle portion oxygen concentration is specified by estimation as described above, it is advantageous in terms of cost as compared with the case where a sensor is provided, and the structure can be simplified.

1 Engine body 2 Cylinder 9 Combustion chamber 20 Injector
DESCRIPTION OF SYMBOLS 30 Intake passage 40 Exhaust passage 41 Exhaust gas purification device 51 High pressure EGR device 52 Low pressure EGR device 71 Injection control part (injection control means)
74a Exhaust oxygen concentration calculation unit (exhaust oxygen concentration calculation means)
74b Low pressure EGR side oxygen concentration calculation unit (low pressure EGR side oxygen concentration calculation means)
74c Low pressure EGR gas flow rate calculation unit (low pressure EGR gas flow rate calculation means)
74d Oxygen concentration specifying means after merge (oxygen concentration calculator after merge)
74e Low pressure EGR gas inflow state determination unit (Low pressure EGR gas inflow state determination means)

Claims (5)

An exhaust purification device for purifying exhaust provided in the exhaust passage, and a low pressure EGR device for connecting the portion of the exhaust passage downstream of the exhaust purification device and the intake passage to recirculate exhaust gas to the intake passage And a portion of the exhaust passage upstream of the exhaust purification device and a portion of the intake passage downstream of the connection portion with the low pressure EGR device are connected to recirculate exhaust gas into the intake passage. In a fuel control device for an engine equipped with a high pressure EGR device,
An injector capable of injecting fuel into the cylinder of the engine;
Injection control means for controlling the injection device;
A post-merging oxygen concentration specifying means for specifying an oxygen concentration in a specific portion between the connection portion of the low pressure EGR device and the connection portion of the high pressure EGR device in the intake passage;
Low pressure EGR gas inflow state determination means for determining whether or not low pressure EGR gas, which is exhaust gas recirculated to the intake passage by the low pressure EGR device, flows into the specific part,
The low-pressure EGR gas inflow state determining means determines that the low-pressure EGR gas has flowed into the specific portion when the oxygen concentration specified by the post-merging oxygen concentration specifying means falls below a predetermined value,
The injection control means includes, in at least a part of the operation region, main injection and pre-injection that injects an amount of fuel smaller than the injection amount of the main injection into the cylinder before the main injection. The injection amount of the preceding injection is controlled based on the determination result of the low pressure EGR gas inflow state determining means, and the low pressure EGR gas inflow state determining means causes the low pressure EGR gas to flow into the specific part. An engine fuel control device that increases the injection amount of the preceding injection when it is determined that the injection has started. The fuel control apparatus for an engine according to claim 1,
The engine fuel control apparatus is characterized in that the predetermined value is set to 23%. The engine fuel control device according to claim 1 or 2,
The specific portion is a portion in the vicinity of a throttle valve provided in a portion between the connection portion of the low pressure EGR device and the connection portion of the high pressure EGR device in the intake passage and capable of opening and closing the intake passage. An engine fuel control device. The engine fuel control apparatus according to any one of claims 1 to 3,
Fresh air amount detection means for detecting the amount of fresh air flowing into the intake passage;
Exhaust oxygen concentration calculating means for calculating an exhaust oxygen concentration, which is an oxygen concentration in the exhaust passage, based on the detected fresh air amount and the injection amount injected from the injection device;
Based on the specified exhaust oxygen concentration and the time during which exhaust gas moves from the cylinder to the connection portion of the low pressure EGR device in the intake passage, the gas flowing from the low pressure EGR device to the intake passage at this connection portion Low pressure EGR side oxygen concentration calculating means for calculating a low pressure EGR side oxygen concentration which is an oxygen concentration of
Low pressure EGR gas flow rate calculating means for calculating a low pressure EGR gas flow rate that is the amount of gas recirculated to the intake passage by the low pressure EGR device;
The combined oxygen concentration specifying means is configured to determine the low-pressure EGR gas at the connection portion based on the detected fresh air amount, the specified low-pressure EGR-side oxygen concentration, and the calculated low-pressure EGR gas flow rate. An engine fuel control device that calculates an oxygen concentration of a mixture of fresh air and fresh air and calculates the oxygen concentration of the specific portion based on the calculated oxygen concentration of the mixture. The engine fuel control apparatus according to any one of claims 1 to 4,
An intake air temperature estimating means for estimating the temperature of gas passing through a portion downstream of the connection portion with the high pressure EGR device in the intake air passage;
The injection control means includes
When the engine water temperature, which is the temperature of the cooling water for cooling the engine, is equal to or lower than a preset reference temperature, the injection amount of the preceding injection is controlled based on the determination result of the low pressure EGR gas inflow state determining means,
When the engine water temperature is higher than the reference temperature, the injection amount of the pre-stage injection is controlled based on the temperature estimated by the intake air temperature estimation means regardless of the determination result. Fuel control device.