JP5370274B2 - Diesel engine combustion control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent too late ignition of fuel and to reduces the amount of CO and HC generated during combustion when an intake air temperature is lower by a predetermined temperature than a target temperature, in a diesel engine that employs a PCI combustion system, while preventing a torque reduction due to an accidental fire. <P>SOLUTION: When the intake air temperature is lower by a predetermined temperature than a target intake air temperature and it is detected that the too late ignition occurs, the main injection and early injection is performed earlier (step S8). <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention belongs to a technical field related to a combustion control device for a diesel engine.

  Conventionally, as a combustion system of a diesel engine, a PCI (Premixed compression Ignition) combustion system that can simultaneously reduce NOx and PM (particulate matter), which are harmful components in exhaust gas, is known (see, for example, Patent Document 1). .

  In this combustion method, before the main injection is performed in the vicinity of the compression top dead center, the early injection is performed to promote the mixing of the injected fuel and the air in the cylinder, thereby suppressing the generation of soot. . Further, in this combustion system, by controlling the amount of exhaust gas recirculation (EGR) that returns a part of the exhaust gas to the intake air via the EGR passage, the ignition timing of the fuel is delayed to the vicinity of the compression top dead center. While sufficiently ensuring the mixing time of the fuel and air (suppressing the generation of soot), the combustion temperature is lowered by reducing the intake oxygen concentration to suppress the generation of NOx.

JP 2008-31874 A

  By the way, when the temperature around the engine is low or just after the engine is started, the intake air temperature of the engine may be lower than the target temperature. In this case, for example, it is conceivable to increase the intake air temperature to the target temperature by increasing the amount of hot exhaust gas recirculated to the intake air via the EGR passage (EGR amount). However, if the intake air temperature is too lower than the target temperature, even if the EGR valve is controlled to be fully opened, the intake air temperature is targeted based on the EGR amount limit (engine hardware limit) determined by the cross-sectional area of the EGR passage. There is a problem that the temperature cannot be raised.

  As a result, the ignitability of the fuel deteriorates and over-ignition occurs in which the ignition timing of the fuel is greatly retarded with respect to the target timing. As a result, the combustion temperature decreases, and the CO and HC during combustion are reduced. There is a problem that the generation amount increases or torque loss (torque reduction) occurs due to misfire.

  The present invention has been made in view of such a point, and an object of the present invention is to reduce the amount of fuel in a diesel engine adopting a PCI combustion system in a situation where the intake air temperature is lower than the target temperature by a predetermined temperature or more. The purpose is to prevent late ignition, and thus to suppress the generation of CO and HC during combustion and to prevent torque loss due to misfire.

In order to achieve the above object, according to the present invention, the intake air temperature is lower than the target intake air temperature by a predetermined temperature or more, and the over-ignition ignition detection means sets the fuel ignition timing in the combustion chamber to the target ignition timing. On the other hand , when over-delayed ignition that is delayed for a first predetermined time or more is detected, at least one of the main injection timing and the early injection timing is advanced, and the fuel ignition delay time with respect to the target ignition timing is: When it is longer than the second predetermined time longer than the first predetermined time, the intake oxygen concentration is increased to control the fuel ignition timing to the target ignition timing .

  Specifically, in the first aspect of the invention, prior to the injection by the main injection control means, the main injection control means for mainly injecting fuel near the compression top dead center from the fuel injection valve facing the combustion chamber of the engine, An early injection control means for injecting fuel earlier than the fuel injection valve, and the intake oxygen concentration is controlled based on the engine speed and the engine load so that the fuel ignition timing becomes a target ignition timing near the compression top dead center. And an intake oxygen concentration control means.

And an over-delayed ignition detecting means for detecting an over-delayed ignition in which the ignition timing of the fuel in the combustion chamber is retarded by a first predetermined time or more with respect to the target ignition timing; When the over-ignition detection means detects the over-ignition, the timing of the main injection by the main injection control means and the timing of the early injection by the early injection control means are determined. And a correction control means for executing an advance control of the injection timing , wherein the correction control means has a second predetermined time in which a fuel ignition delay time with respect to the target ignition timing is longer than the first predetermined time. If so, the intake oxygen control for increasing the intake oxygen concentration is further executed by the oxygen concentration control means so as to control the fuel ignition timing to the target ignition timing. It assumed to have been made.

  According to this configuration, when the intake air temperature is lower than the target temperature by a predetermined temperature or more, such as during cold start, and when the over-delayed ignition of the fuel is detected by the over-delayed ignition detecting means, the correction control means The injection timing advance control is executed. As a result, at least one of the timing of the main injection by the main injection control means and the timing of the early injection by the early injection control means is advanced, whereby the ignition timing of the fuel is advanced to prevent over-ignition ignition. As a result, generation of CO and HC accompanying excessively late ignition and torque loss due to misfire can be suppressed.

For example, if the ignition delay time is so long that the fuel ignition timing cannot be controlled to the target ignition timing even if the injection timing advance control is executed by the correction control means, the intake oxygen control is performed by the oxygen concentration control means. By executing, the fuel ignition timing can be surely advanced to the target ignition timing.

In the invention of claim 2, in the invention of claim 1 Symbol placement, the correction control means further is in a low state or a predetermined temperature with respect to the intake air temperature is a target intake air temperature, and, by the over-retarded ignition detecting means When excessively late ignition is detected, the main injection by the main injection control means is reduced, while the injection amount control for increasing the early injection by the early injection control means is further executed.

  According to this configuration, when the intake air temperature is lower than the target intake air temperature by a predetermined temperature or more and overdelayed ignition is detected by the overdelayed ignition detecting unit, the correction control unit compares it with the main injection. Thus, the early injection, which has the effect of advancing the ignition timing, is increased, while the main injection is decreased. As a result, it is possible to reliably advance the ignition timing of the fuel to the target ignition timing while preventing a decrease in the output torque of the engine.

According to a third aspect of the present invention, in the second aspect of the invention, the early injection by the early injection control means is divided injection in which fuel is injected in a plurality of times.

  According to this, by performing the early injection by the early injection control means by the divided injection, it is possible to further promote the premixing of the fuel injected early and suppress the generation of soot.

According to the invention of claim 4, in the invention of claim 3 , the injection amount control by the correction control means reduces the main injection by the main injection control means, while being the earliest among a plurality of fuel injections in the early injection. It is assumed that the control is to increase the amount of injection performed at the time.

  According to this, the injection amount control is executed by the correction control means so as to increase the injection performed at the earliest time among the plurality of fuel injections in the early injection. As a result, the ignition timing of the fuel can be advanced more reliably, and generation of CO and HC and torque loss due to misfire can be prevented.

According to a fifth aspect of the present invention, in the first aspect of the invention, the apparatus further comprises after-injection control means for after-injecting fuel from the fuel injection valve after main injection by the main injection control means, and the correction control means further includes When performing the injection timing advance control, it is assumed that the after injection by the after injection control means is reduced while the injection amount control for increasing the early injection by the early injection control means is executed.

  According to this configuration, the soot generated with the combustion of the main-injected fuel can be burned together with the after-injected fuel, so that the amount of soot generated can be reduced as much as possible. When executing the injection amount control by the correction control means, the after injection is reduced without reducing the main injection having a large contribution to the torque, while the early injection having a large advance effect of the ignition timing is increased. As a result, it is possible to reliably advance the ignition timing of the fuel to the target ignition timing while preventing a decrease in torque.

According to a sixth aspect of the invention, in the first aspect of the invention, the apparatus further comprises after-injection control means for after-injecting fuel from the fuel injection valve after main injection by the main injection control means, and the correction control means further includes When performing the injection timing advance control, the after injection by the after injection control means is reduced, while the injection amount control for increasing the main injection by the main injection control means is executed.

  According to this configuration, the soot generated with the combustion of the main-injected fuel can be burned together with the after-injected fuel, so that the amount of soot generated can be reduced as much as possible. The correction control means reduces the after-injection, while increasing the main injection that contributes greatly to the torque, thereby preventing excessive mixing of the fuel due to early injection and preventing the diesel knock during combustion. While suppressing the generation, the ignition timing of the fuel can be surely advanced to the target ignition timing.

According to a seventh aspect of the present invention, in the invention according to any one of the second to sixth aspects, the intake oxygen concentration control means includes an EGR amount control means for controlling an EGR amount, and the correction control means further includes an EGR amount. Is configured to execute the injection timing advance control even when excessive retard ignition is detected by the excessive retard detection means. And

  According to this configuration, when the over-ignition detection is detected by the over-ignition detection means and the EGR amount is larger than the target amount by a predetermined amount or more, the injection timing advance control is performed by the correction control means. Is executed.

  By the way, the adjustment of the EGR amount is normally performed by adjusting the opening degree of the EGR valve. However, since the control response of the EGR amount by the EGR valve is generally low, the EGR valve is closed according to the operating state of the engine. Even if it is controlled to the side, since there is a time lag until the EGR amount actually decreases (intake oxygen concentration increases), the intake oxygen concentration temporarily reaches the target during the transition period when the EGR valve is controlled to close. It becomes lower than the concentration, and over-ignition tends to occur. As a result, there is a problem that the ignition delay time of the fuel increases, the amount of CO and HC generated increases, and torque loss due to misfire occurs.

  In contrast, in the present invention, when the EGR amount is larger than the target amount by a predetermined amount or more, as described above, the injection timing advance control is executed by the correction control means, and the main injection control means performs the main injection control. At least one of the timing and the timing of early injection by the early injection control means is advanced. Thereby, the fuel ignition timing can be advanced as a whole and controlled to the target ignition timing. Therefore, the combustion temperature can be raised as much as possible to reliably prevent generation of CO and HC during fuel and torque loss due to misfire.

According to an eighth aspect of the present invention, in the seventh aspect of the present invention, the correction control means further includes a difference between the EGR amount and a target amount equal to or greater than a predetermined threshold amount larger than the predetermined amount, or the intake air. When the difference between the temperature and the target temperature is equal to or higher than a predetermined threshold temperature that is higher than the predetermined temperature, the injection timing advance is performed regardless of whether or not the excessively late ignition detecting means detects excessively delayed ignition. It is assumed that any one of the control, the injection amount control, and the intake oxygen control is executed.

  According to this configuration, even if no excessively late ignition has occurred at this time, if it is predicted that it will occur in the future, that is, the difference between the EGR amount and the target amount is not less than the predetermined amount, or When the difference between the intake air temperature and the target temperature is equal to or higher than the predetermined temperature, the injection timing advance control is performed by the correction control unit regardless of whether or not the over-delay ignition detection unit detects over-delay ignition. In addition, any one of the injection amount control and the intake oxygen control is executed, so that it is possible to prevent over-ignition from occurring. Therefore, not only the generation of CO and HC can be suppressed, but also torque loss due to misfire can be prevented before the vehicle occupant feels it.

As described above, according to the combustion control device for a diesel engine of the present invention, the intake air temperature is lower than the target intake air temperature by a predetermined temperature or more, and the over-ignition detection means causes the ignition of fuel in the combustion chamber. When over-delayed ignition is detected in which the timing is delayed by a first predetermined time or more with respect to the target ignition timing, at least one of the main injection timing and the early injection timing is advanced, and the fuel with respect to the target ignition timing is When the ignition delay time is equal to or longer than the second predetermined time longer than the first predetermined time, the intake oxygen concentration is increased so as to control the fuel ignition timing to the target ignition timing. In a diesel engine adopting the PCI combustion method, under the condition that the intake air temperature is lower than the target temperature, the fuel is prevented from being ignited too late. And thereby suppress the generation of HC, it is possible to prevent the loss torque due to misfire. When the ignition delay time is equal to or longer than the second predetermined time, the fuel ignition timing can be reliably advanced to the target ignition timing by increasing the intake oxygen concentration.

It is the schematic which shows the whole structure of the combustion control apparatus of the diesel engine which concerns on embodiment of this invention. It is the graph which showed the mode of change of in-cylinder temperature which changes with advance of a crank angle in fuel injection timing in normal PCI combustion mode. FIG. 5 is a graph showing the fuel injection timing and the change in the in-cylinder temperature that changes with the progress of the crank angle, and (a) shows the excess before the first correction control is executed in the PCI combustion mode. A state in which the late ignition occurs is shown, and (b) shows a state after the first correction control is executed in the PCI combustion mode. FIG. 6 is a graph showing a fuel injection timing and a state of a change in in-cylinder temperature that changes with the progress of the crank angle, in which (a) shows an excess before executing the second correction control in the PCI combustion mode. The state where the slow ignition has occurred is shown, and (b) shows the state after the second correction control is executed in the PCI combustion mode. FIG. 6 is a graph showing the fuel injection timing and the state of change in the in-cylinder temperature that changes as the crank angle advances, and (a) shows the excess before the third correction control is executed in the PCI combustion mode. The state where the slow ignition has occurred is shown, and (b) shows the state after shifting to the diffusion combustion mode by the execution of the third correction control. It is a flowchart which shows the combustion control process performed by ECU in PCI combustion mode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of an engine exhaust gas purification apparatus A according to an embodiment of the present invention. Reference numeral 1 denotes a diesel engine mounted on a vehicle. This engine 1 has a plurality of cylinders 2, 2,... (Only one is shown), and a piston 3 is fitted into each cylinder 2 so as to be reciprocable. The combustion chamber 4 is partitioned. In addition, an injector 5 (fuel injection valve) is disposed on the ceiling of the combustion chamber 4, and high-pressure fuel is directly injected into the combustion chamber 4 from the nozzle at the tip. In the present embodiment, as will be described in detail later, the engine 1 has two modes: a PCI combustion mode in which fuel combustion in the combustion chamber 4 is performed by PCI combustion and a diffusion combustion mode in which diffusion combustion is performed by diffusion combustion. Yes.

  The configuration for supplying fuel to the injector 5 for each cylinder 2 is not shown, but is a so-called common rail type having a common fuel distribution pipe (common rail) to which each injector 5 is connected. An output signal of a fuel pressure sensor for detecting the fuel pressure (common rail pressure) is input to the ECU 100 described later, and the ECU 100 controls the common rail pressure.

  A valve operating mechanism (not shown) that opens and closes the intake valve 18 and the exhaust valve 19 is disposed at the top of the engine 1.

  An intake passage 6 for supplying air (fresh air) filtered by an air cleaner 29 to the combustion chamber 4 of each cylinder 2 is connected to one side (right side in the figure) of the engine 1. The intake passage 6 has a first compressor 9 and a second compressor 10 that are driven by a first turbine 7 and a second turbine 8 described later in order from the upstream side to the downstream side, respectively, and compress the intake air. An intercooler 12 for cooling the intake air compressed by the two compressors 9 and 10 and an intake throttle valve 13 are provided.

  On the other hand, an exhaust passage 14 for discharging combustion gas (exhaust gas) from the combustion chamber 4 of each cylinder 2 is connected to the opposite side (left side in the figure) of the engine 1. The upstream end portion of the exhaust passage 14 is an exhaust manifold that branches into each cylinder 2 and communicates with the combustion chamber 4 through an exhaust port. The exhaust passage 14 downstream from the exhaust manifold has a downstream side from the upstream side. The first oxidation turbine 7 and the second turbine 8 that are rotated in response to the exhaust flow, and the diesel oxidation catalyst (DOC) that can purify harmful components (HC, CO, NOx, soot, etc.) in the exhaust. 15 and DPF (Diesel Particulate Filter) 16 are disposed. The DPF 16 is made of a heat-resistant ceramic material made of silicon carbide (SiC), cordierite, or the like into a three-dimensional network structure or a wall-through type honeycomb structure. In the process of passing through the DPF, it is collected by the DPF.

  The first compressor 9 and the first turbine 7 are connected to each other in a rotationally integrated manner to form a first exhaust turbocharger 20. Similarly, the second compressor 10 and the second turbine 8 are connected to each other in a rotationally integrated manner. Thus, the second exhaust turbocharger 21 is configured. As described above, by providing the two exhaust turbochargers 20 and 21, it is possible to improve the supercharging efficiency.

  The exhaust passage 14 includes a first exhaust bypass passage 22 that bypasses the turbine 7 of the first exhaust turbocharger 20 and a second exhaust bypass passage 23 that bypasses the turbine 8 of the second exhaust turbocharger 21. It is connected. A regulating valve 24 for adjusting the amount of exhaust gas flowing to the first exhaust bypass passage 22 is disposed at the upstream end of the first exhaust bypass passage 22, and at the upstream end of the second exhaust bypass passage 23, A waste gate valve 25 for adjusting the amount of exhaust flowing to the second exhaust bypass passage 23 is provided. An intake bypass passage 27 that bypasses the compressor 9 of the first exhaust turbocharger 20 is connected to the intake passage 6, and the intake bypass passage 27 is used to adjust the amount of air flowing to the intake bypass passage 27. An intake bypass valve 28 is provided.

  An upstream end of an EGR passage 30 for returning a part of the exhaust gas to the intake side is connected to a portion of the exhaust passage 14 upstream of the first exhaust turbocharger 20. The EGR passage 30 includes a cold EGR passage 31 for recirculating the relatively low temperature exhaust gas and a hot EGR passage 32 for recirculating the high temperature exhaust gas. The passage 6 is connected to a portion between the intake throttle valve 13 and the surge tank 26. In the present embodiment, a polar cold EGR passage 33 is further provided for recirculating the exhaust gas having a temperature lower than that of the exhaust gas passing through the cold EGR passage 31. The upstream end of the polar cold EGR passage 33 is connected to a portion of the exhaust passage 14 between the DPF 16 and the silencer 17, and the downstream end of the polar cold EGR passage 33 is connected to the second exhaust turbocharger 21 in the intake passage 6. It is connected to a part upstream of the position. The EGR passages 31 to 33 are respectively provided with EGR valves 34 to 36 whose opening degree can be adjusted. Further, an EGR cooler 40 for cooling the exhaust gas passing through the inside thereof is disposed in each of the intermediate portions of the cold EGR passage 31 and the polar cold EGR passage 33.

  Each of the injector 5, the intake throttle valve 13, the EGR valves 34 to 36, the regulator valve 24, the wastegate valve 25, etc. receives control signals from a control unit (Electronic Control Unit: hereinafter referred to as ECU) 100. Works.

  The ECU 100 is mainly composed of a microcomputer, and has a known CPU, ROM, RAM, and the like. The ECU 100 includes at least a crank angle sensor 51 that detects the rotation angle of the crankshaft of the engine 1, an intake pressure sensor 52 that detects the pressure state of the intake air, an oxygen concentration sensor 53 that detects the oxygen concentration in the exhaust, and a combustion chamber. A finger pressure sensor 54 for detecting the pressure of the air, an air flow sensor 55 for detecting the flow rate of air sucked into the engine 1 from the outside, an intake air temperature sensor 56 for detecting the temperature of the intake air after EGR gas mixing, an accelerator pedal (not shown) An accelerator opening sensor 57 that detects the amount of stepping (accelerator opening), an oxygen concentration sensor 58 that detects the oxygen concentration of the intake air supplied to the combustion chamber, and a catalyst temperature for detecting the temperature of the diesel oxidation catalyst 15 Output signals from the sensor 59 and the differential pressure detection sensor 60 for detecting the differential pressure between the upstream side and the downstream side of the DPF 16 are They are respectively input.

  The ECU 100 executes the switching between the PCI combustion mode and the diffusion combustion mode in accordance with the operation state of the engine 1 based on signals from various sensors.

(About engine supercharging control)
The ECU 100 controls the openings of the intake bypass valve 28, the regulator valve 24, and the waste gate valve 25 to the openings set according to the operating state of the engine 1. In the present embodiment, the ECU 100 operates the intake bypass in order to operate only the second exhaust turbocharger 21 because the first exhaust turbocharger 20 becomes exhaust resistance in an operation region on a high load or high rotation side. The valve 28 and the regulating valve 24 are fully opened, and the wastegate valve 25 is set to an opening degree close to a fully closed state. The ECU 100 controls the intake bypass valve 28 and the regulating valve 24 to the closed side as the operation state of the engine 1 approaches the operation region on the low load or low rotation side, and the first and second exhaust turbochargers 20. , 21 are activated. Thus, the ECU 100 controls the intake bypass valve 28, the regulator valve 24, and the waste gate valve 25 to be in a substantially fully closed state in a low load or low rotation side operation region in which a PCI combustion mode to be described later is executed. Therefore, in the present embodiment, in the PCI combustion mode, in order to control the intake oxygen concentration, there is almost no margin for controlling the opening degree of the regulating valve 24 and the wastegate valve 25 (controlling the supercharging pressure), and the intake air The oxygen concentration is controlled mainly by opening control of the EGR valves 34 to 36.

(About engine combustion control)
The ECU 100 executes the engine control based on the diffusion combustion by selecting the diffusion combustion mode on the high load or high rotation side, and executes the engine control based on the PCI combustion by selecting the PCI combustion mode on the low load or low rotation side. It is supposed to be. In addition, when the PCI combustion mode is selected, the ECU 100 performs combustion control of the engine 1 by switching to the diffusion combustion mode as necessary, such as when the catalyst temperature is lower than a reference value.

  The combustion control of the engine 1 in the PCI combustion mode is basically performed in the vicinity of the compression top dead center (for example, BTDC 35 ° to BTDC 5 ° and BTDC 15 ° in the present embodiment) as shown in FIG. Prior to the main injection, a small amount of fuel injection (hereinafter referred to as early injection) is performed relatively early to secure an ignition delay time from early injection to ignition and promote mixing of fuel and air (so-called By promoting premixed combustion), the generation of soot is suppressed, and the ignition timing is set to the target ignition timing (compression top dead center in the present embodiment) in combination with the control of the EGR amount equivalent to the intake oxygen concentration. By controlling and raising the combustion temperature as much as possible, the generation of CO and HC is suppressed, and torque reduction due to misfire is prevented. The EGR amount is controlled by controlling the opening degree of the EGR valves 34 to 36 based on the engine speed and the engine load so that the high temperature portion of the combustion mixture becomes lower than the NOx generation temperature. Is called. Further, in this combustion control, after injection is performed after the main injection, soot generated with the combustion of the main injection is burned by the after injection.

  In the present embodiment, on the premise of such control, in particular, when the ignition delay time is long, that is, when the ignition timing is delayed by the first predetermined time T1 or more with respect to the target ignition timing, the ignition timing is set to the target ignition timing. Correction control for advancing (control of steps S8, S11 and S12 described later) is executed.

  The correction control includes a first correction control (see FIG. 3) and a second correction control (see FIG. 4) performed while maintaining PCI combustion, and a third correction performed by switching from PCI combustion to diffusion combustion. There are three controls: control (see FIG. 5). (A) in each figure shows a state in which the over-ignition ignition occurs before executing the correction control, and (b) in each figure shows a state in which the over-ignition ignition after the execution of the correction control is eliminated. Yes.

  In the first correction control, as shown in FIG. 3B, after injection is stopped (the injection amount of after injection is reduced to 0) and the main injection is increased by that amount, and the entire injection timing is set. This is performed in combination with the injection timing advance control for making the advance advance. In the injection timing advance control in this embodiment, both the early injection and the main injection are advanced by the same amount (for example, 3 ° to 5 ° CA). Only one of the early injection and the main injection may be advanced.

  Further, the second correction control is oxygen concentration control that decreases the EGR amount and increases the intake oxygen concentration, and does not correct the injection amount or the injection timing as shown in FIG.

As will be described later, the first correction control is executed when the ECU 100 determines that the ignition delay time with respect to the target ignition timing is less than the injection control possible time T2, and the second correction control is executed by the ECU 100. This is executed when it is determined that the ignition delay time is equal to or longer than the injection control possible time T2.

  As described above, the third correction control is performed by switching from the PCI combustion mode to the diffusion combustion mode (see FIG. 5B). Combustion control in this diffusion combustion mode is such that the fuel atomized by the main injection performed near the compression top dead center (ATDC 5 ° to 20 ° in this embodiment) diffuses and diffuses and burns while taking in surrounding air. It is a thing. Further, in this combustion mode, a small amount of pilot injection is performed before compression top dead center (BTDC 15 ° in this embodiment) prior to main injection, thereby improving the ignitability of main injection and delaying ignition of main injection. To shorten. In this combustion mode, diffusion combustion is mainly used, so that a large amount of EGR for securing the ignition delay time is not required unlike the PCI fuel mode. Therefore, in this diffusion combustion mode, the amount of EGR is reduced as compared with the PCI combustion mode, and as a result, the intake oxygen concentration can be increased as compared with the PCI combustion mode. As a result, the combustion temperature is increased compared with the PCI combustion mode. Maintaining a high temperature can suppress the generation of CO and HC.

  Next, details of the combustion control of the engine 1 in the ECU 100 will be described in detail based on the flowchart of FIG.

  First, in the first step S1, signals from various sensors 51-60 are read.

  In step 2, the intake air temperature is calculated based on the signal from the intake air temperature sensor 56 read in step 1, and it is determined whether or not the calculated intake air temperature is lower than the target temperature. When this determination is NO, the process returns, while when it is YES, the process proceeds to Step 3.

  In step 3, it is determined whether or not the intake air temperature is lower than the target temperature by a predetermined temperature K or more. If this determination is NO, the process returns. If YES, the process proceeds to step 4. Here, when the intake air temperature is lower than the target temperature by the predetermined temperature K or more, for example, even if the EGR valve 35 of the hot EGR passage 32 is controlled to be fully opened, the EGR amount determined from the passage cross-sectional area of the EGR passage 32, etc. This means that the intake air temperature is below the target temperature so that the intake air temperature cannot be controlled to the target temperature due to the limit (hardware limit of the engine 1).

  In step 4, the time variation of the in-cylinder pressure is obtained based on the signal from the finger pressure sensor 54, the fuel ignition timing is calculated based on the obtained pressure change, and the ignition delay time with respect to the target ignition timing is calculated. To do.

  In step S5, it is determined whether or not the ignition delay time calculated in step S4 is equal to or longer than the first predetermined time T1, and when the determination is NO, the process returns. On the other hand, when the determination is YES, the over-ignition ignition is performed. The process proceeds to step S6. Here, the first predetermined time T1 is a lower limit value of the ignition delay time such that the amount of CO and HC generated during combustion is equal to or greater than an allowable value.

  In step S6, the temperature of the oxidation catalyst (DOC) 15 is calculated (estimated) based on the signal from the catalyst temperature sensor 59, and it is determined whether or not the calculated oxidation catalyst temperature exceeds the reference temperature. When the determination is NO, the process proceeds to step S12, and when the determination is YES, the process proceeds to step S7. This reference temperature is the activation temperature of the oxidation catalyst 15 in this embodiment.

  In step S7, it is determined whether or not the ignition delay time calculated in step S4 is less than the injection controllable time T2. If this determination is NO, the process proceeds to step S11, and if YES, the process proceeds to step S8.

  In step S8, the injector 5 is controlled so that after injection is stopped and the main injection is increased by that amount (injection amount control is executed), and both early injection and main injection are performed according to the ignition delay time. The injector 5 is controlled to advance the injection timing (injection timing advance control). In this embodiment, the advance amount of the injection timing is increased as the ignition delay time is longer.

  In step S9, it is determined whether or not the intake air temperature has reached the target temperature after a predetermined time has elapsed. When this determination is NO, the process returns to step S7, and when it is YES, the process proceeds to step S10.

  In step S10, the process returns to the normal PCI mode (that is, PCI control (see FIG. 2) in which the correction control in steps S8 and S11 is not performed), and then returns.

  In step S11, the target intake oxygen concentration is determined according to the ignition delay time calculated in step S4 in step S8, and the opening degree of each EGR valve 34 to 36 is controlled to the closed side so as to be the target intake oxygen concentration. To do. The opening ratio of each EGR valve 34 to 36 may be controlled to an opening ratio set in advance according to the target intake air temperature. The target inspiratory oxygen concentration is mapped in advance and stored in the ROM using the engine speed and the engine load as parameters so that the target inspiratory oxygen concentration increases as the ignition delay time increases.

  In step S12, the control mode of the engine 1 is switched from the PCI combustion mode to the diffusion combustion mode, and then the process returns.

  As described above, in the above-described embodiment, the ECU 100 assumes that the combustion temperature control of the engine 1 is performed in the PCI combustion mode in the low load to low rotation operation region, and the intake air temperature is the predetermined temperature K with respect to the target intake air temperature. When it is detected that the ignition timing is low and excessively late ignition has occurred, the injection timing advance control and the injection amount control are performed in order to advance the ignition timing and control it to the target ignition timing. The combined first correction control is executed (the process of step S8 is executed).

  As described above, the ignition timing is advanced by the fuel injection control by the injector 5, so that the ignition timing is advanced with high responsiveness compared to the case where the ignition timing is advanced by, for example, opening / closing control of the EGR valve. It can be controlled to the corner side. Accordingly, it is possible to prevent the occurrence of CO and HC while the advance timing of the ignition timing is delayed, or the occurrence of torque reduction due to misfire.

  Here, when executing the injection amount control, the ECU 100 compensates for the decrease in the fuel injection amount due to the stop of the after injection by the increase in the main injection, so that the engine torque can be prevented from decreasing. . Further, since the reduced amount of the after injection is added to the main injection instead of the early injection, it is possible to prevent the occurrence of knocking due to excessive progress of fuel premixing.

  Even when the ECU 100 detects that the intake air temperature is lower than the target intake air temperature by a predetermined temperature K or more and over-ignition has occurred, the ignition delay time is the injection control possible time T2. If this is the case (if the determination in step S7 is NO), in order to advance the ignition timing, instead of executing the injection control of the injector 5 as described above, the intake oxygen control is executed. The EGR valves 34 to 36 are controlled to the closed side. As a result, even when the fuel ignition timing cannot be controlled to the target ignition timing by the injection control of the injector 5, the fuel ignitability is improved by reducing the EGR amount and increasing the intake oxygen concentration. The time can be advanced to the target time.

Further, even when the ECU 100 detects that the intake air temperature is lower than the target intake air temperature by a predetermined temperature K or more and over-ignition occurs, the oxidation catalyst temperature is lower than the reference temperature. If this is the case (if the determination in step S6 is NO), the third correction control is executed to switch the combustion mode of the engine 1 to the diffusion combustion mode. In the diffusion combustion mode, as described above, since the combustion temperature is higher than that in the PCI combustion mode, the generation of CO and HC at the time of combustion can be greatly reduced, and the oxidation catalyst 15 can be utilized using high-temperature exhaust gas. Can help to warm up.
(Other embodiments)
The configuration of the present invention is not limited to the above embodiment, but includes various other configurations. That is, in the above embodiment, only the oxygen concentration control is executed in the process of step S11 that proceeds when the determination in step S7 is NO, but the injection timing advance control and the injection amount control are executed together. You may make it do. As a result, even when excessively late ignition occurs, the fuel ignition timing can be reliably advanced to the target ignition timing.

  In the above embodiment, when the injection amount control by the ECU 100 is performed, the main injection is increased by the amount after the after injection is stopped. However, the early injection may be increased.

  Moreover, in the said embodiment, although the early injection in PCI combustion mode is single injection performed by one injection, it is good also as division injection which injects fuel in multiple times, for example. Thereby, mixing of fuel by early injection can be further promoted, and generation of soot at the time of combustion can be reliably suppressed. Thus, in the injection amount control in the case where the early injection is divided injection, it is preferable to increase the injection to be performed at the earliest time among a plurality of fuel injections in the early injection. In this way, the fuel ignition timing can be surely advanced to the target ignition timing.

  In the above embodiment, the correction control is executed when the ECU 100 detects over-ignition ignition. However, in the ECU 100, the difference between the EGR amount and the target amount is a predetermined threshold amount LM (> location). If it is determined that the difference between the intake air temperature and the target temperature is equal to or greater than a predetermined threshold temperature LK (> predetermined temperature K), whether or not over-ignition ignition has been detected. Regardless, any one of the injection timing advance control, the injection amount control, and the intake oxygen control may be executed. Thus, under a situation where it is predicted that excessively late ignition will occur in the future, the ECU 100 can execute the respective controls in advance and advance the ignition timing before the excessively delayed ignition occurs. Thus, excessively late ignition can be prevented in advance, so that torque loss due to generation of CO and HC and misfire can be more reliably suppressed.

  In the above embodiment, after injection is performed after main injection in the normal PCI combustion mode, it is not always necessary to perform after injection. When the after injection is not performed, the injection amount control by the ECU 100 may be such that the main injection is reduced and the early injection is increased accordingly.

  In the above embodiment, when the ECU 100 executes the oxygen concentration control, the opening degree of the EGR valves 34 to 36 is controlled in order to control the intake oxygen concentration, but for example, the waste gate valve 25 and the regulator are controlled. The intake oxygen concentration may be controlled by controlling the opening degree of the rate valve 24. In this case, the regulating valve 24, the waste gate valve 25, and the ECU 100 constitute an intake oxygen concentration control means. Furthermore, the intake oxygen concentration may be controlled by controlling the opening / closing timing of the intake valve 18 and the exhaust valve 19 in combination with the EGR control. In this case, the intake valve 18, the exhaust valve 19, and the EGR valves 34 to 36 constitute intake oxygen concentration control means.

  Furthermore, in the above embodiment, the supercharging pressure is controlled by controlling the wastegate valve 25 and the regulating valve 24. For example, a variable nozzle turbo (VGT) in which a variable nozzle is provided on the upstream side of the turbine. May be adopted.

  Furthermore, in the above embodiment, when the injection amount control is executed by the ECU 100, the after injection is stopped. However, the after injection may be reduced without completely stopping.

  The present invention is useful for a combustion control device for a diesel engine, and is particularly useful when applied to a diesel engine employing a PCI combustion system.

A Diesel engine combustion control device T1 first predetermined time T2 injection control possible time (second predetermined time)
K predetermined temperature M predetermined amount LM predetermined threshold amount LK predetermined threshold temperature 1 engine 4 combustion chamber 5 injector (fuel injection valve)
34 EGR valve (EGR amount control means, intake oxygen concentration control means)
35 EGR valve (EGR amount control means, intake oxygen concentration control means)
36 EGR valve (EGR amount control means, intake oxygen concentration control means)
54 Acupressure sensor (excessive ignition detection means)
100 ECU (main injection control means, early injection control means, excessively late ignition detection means,
Correction control means, EGR amount control means, intake oxygen concentration control means)

Claims (8)

Main injection control means for main injection of fuel near the compression top dead center from the fuel injection valve facing the combustion chamber of the engine, and early injection for early injection of fuel from the fuel injection valve prior to injection by the main injection control means A diesel engine comprising: a control means; and an intake oxygen concentration control means for controlling the intake oxygen concentration based on the engine speed and the engine load so that the fuel ignition timing is a target ignition timing in the vicinity of compression top dead center A combustion control device of
An over-delayed ignition detecting means for detecting an over-delayed ignition in which the ignition timing of the fuel in the combustion chamber is delayed by a first predetermined time or more with respect to the target ignition timing;
When the intake air temperature is lower than the target intake air temperature by a predetermined temperature or more and overdelayed ignition is detected by the overdelayed ignition detecting unit, the timing of the main injection by the main injection control unit and the early injection further comprising a correction control means for performing the injection timing advance control to advance at least one of the timing of the early injection by the control means,
When the fuel ignition delay time with respect to the target ignition timing is equal to or longer than a second predetermined time longer than the first predetermined time, the correction control means sets the target fuel ignition timing by the oxygen concentration control means. A combustion control apparatus for a diesel engine, characterized by further performing intake oxygen control for increasing the intake oxygen concentration so as to be controlled at an ignition timing . The combustion control apparatus according to claim 1 Symbol placement of the diesel engine,
The correction control means is further configured so that when the intake air temperature is lower than the target intake air temperature by a predetermined temperature or more and overdelay ignition is detected by the overdelay ignition detection means, the main injection control means performs main control. A diesel engine combustion control device configured to further execute injection amount control for reducing the amount of injection while increasing the amount of early injection by the early injection control means. The diesel engine combustion control apparatus according to claim 2 ,
2. The diesel engine combustion control apparatus according to claim 1, wherein the early injection by the early injection control means is divided injection in which fuel is injected in a plurality of times. In the diesel engine combustion control device according to claim 3 ,
The injection amount control by the correction control means is a control for reducing the main injection by the main injection control means and increasing the injection to be performed at the earliest time among a plurality of fuel injections in the early injection. Diesel engine combustion control device. The combustion control apparatus according to claim 1 Symbol placement of the diesel engine,
After the main injection by the main injection control means, further comprising after injection control means for after-injecting fuel from the fuel injection valve,
Further, when executing the injection timing advance control, the correction control means reduces the after injection by the after injection control means while executing the injection amount control for increasing the early injection by the early injection control means. A combustion control device for a diesel engine, characterized in that it is configured. The combustion control apparatus according to claim 1 Symbol placement of the diesel engine,
After the main injection by the main injection control means, further comprising after injection control means for after-injecting fuel from the fuel injection valve,
The correction control means further executes an injection amount control for increasing the main injection by the main injection control means while reducing the after injection by the after injection control means when executing the injection timing advance control. A combustion control device for a diesel engine, characterized in that it is configured. In the combustion control apparatus of the diesel engine as described in any one of Claims 2-6 ,
The intake oxygen concentration control means includes an EGR amount control means for controlling the EGR amount,
The correction control means further performs the injection timing advance control when the EGR amount is larger than the target amount by a predetermined amount or more and the over-delayed ignition detection means detects over-delayed ignition. A combustion control device for a diesel engine, characterized by being configured to execute. The diesel engine combustion control device according to claim 7 ,
The correction control means further has a difference between the EGR amount and the target amount equal to or greater than a predetermined threshold amount larger than the predetermined amount, or a difference between the intake air temperature and the target temperature is higher than the predetermined temperature. When the temperature is higher than a predetermined threshold temperature, any one of the injection timing advance control, the injection amount control, and the intake oxygen control is performed regardless of whether or not the over-delayed ignition detection means detects over-delayed ignition. A combustion control apparatus for a diesel engine, characterized in that the system is configured to execute the above.

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