Control device and control method for multi-cylinder compression ignition type internal combustion engine

Abstract

To prevent two injectors from becoming open simultaneously during post injection, in a multi-cylinder compression ignition type internal combustion engine.SOLUTION: An engine has four cylinders, and an ignition order is #1→#3→#4→#2. An engine ECU performs multi-stage post-injection, which injects fuel in an expansion stroke during DPF regeneration control. The engine ECU sets post-injection timing so that an exhaust temperature of the engine does not exceed a predetermined temperature. When the post-injection timing overlaps with pilot injection of the next cylinder (#3), the multi-stage post-injection timing overlapping with the pilot injection is retarded to after main injection of the next cylinder (#3) (Fig.3(A)). When the post-injection timing overlaps with the pilot injection of the next cylinder (#3), the timing of all multi-stage post-injections may be retarded to after the main injection of the next cylinder (#3) (Fig.3(B)).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a control device for a multi-cylinder compression ignition internal combustion engine and a control method for a multi-cylinder compression ignition internal combustion engine. [Background technology]

[0002] As we move toward a decarbonized society, the use of carbon-neutral biofuels and synthetic fuels (e-fuels) with low environmental impact is expanding. For example, biofuel-blended diesel fuel, which is made by blending diesel fuel with biodiesel fuel made from rapeseed oil or waste cooking oil, is used as fuel for compression-ignition internal combustion engines (diesel engines). Hydrotreated vegetable oil (HVO), which is made by adding hydrogen to vegetable oil and hydrocracking it, is also sometimes used as fuel for diesel engines.

[0003] For example, in order to remove particulates that have accumulated on a particulate filter installed in the exhaust passage and regenerate the particulate filter, post-injection, in which fuel is injected into the cylinder (combustion chamber) during the expansion stroke (combustion expansion stroke) of an internal combustion engine, may be performed. HVO has a higher cetane number than diesel and is prone to self-ignition. For example, if HVO is used as fuel and post-injected at the same post-injection timing as diesel, the HVO may burn in the cylinder, causing the exhaust gas temperature to rise when it is emitted from the internal combustion engine. If the exhaust gas temperature rises excessively, there is a concern that it may exceed the designed heat resistance temperature of exhaust system components (especially the exhaust manifold).

[0004] Japanese Patent Application Laid-Open Publication No. 2010-096056 (Patent Document 1) describes detecting the cetane number of fuel, and retarding the post-injection timing as the cetane number increases. Patent Document 1 states that by retarding the post-injection timing, the amount of fuel burned in the cylinder during post-injection (combustion amount) decreases, even when the fuel has a high cetane number. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-069056 Summary of the Invention [Problem to be solved by the invention]

[0006] If the post-injection timing is retarded, it may overlap with the fuel injection of the next cylinder. In this case, the post-injection and the fuel injection of the next cylinder must be performed simultaneously, and two fuel injection valves (injectors) must be opened simultaneously to inject fuel.

[0007] The injectors are controlled to open and close by a drive circuit. When two injectors are opened and closed at the same time, there is a concern that the drive circuit may not have enough power.

[0008] An object of the present disclosure is to prevent two injectors from opening simultaneously during post injection in a multi-cylinder compression ignition internal combustion engine. [Means for solving the problem]

[0009] (1) The control device for the multi-cylinder compression ignition internal combustion engine disclosed herein performs post-injection, which injects fuel during the expansion stroke, and sets the post-injection timing so that the exhaust gas temperature does not exceed a predetermined temperature.If the post-injection timing overlaps with the fuel injection of the next cylinder, the post-injection timing is retarded so that the post-injection does not overlap with the fuel injection of the next cylinder.

[0010] When post-injection is performed in which fuel is injected during the expansion stroke, if the fuel has a high cetane number and is easily self-ignited, the post-injected fuel is more likely to burn in the cylinder, resulting in a high exhaust gas temperature. Retarding the post-injection timing makes it more difficult for the fuel to burn in the cylinder. With this configuration, the control device performs post-injection in which fuel is injected during the expansion stroke, and sets the post-injection timing so that the exhaust gas temperature does not exceed a predetermined temperature. Because the post-injection timing is set to the retarded side so that the exhaust gas temperature does not exceed the predetermined temperature, even if the fuel has a high cetane number, combustion of the post-injected fuel in the cylinder can be suppressed, thereby suppressing an excessive rise in the exhaust gas temperature.

[0011] If the post-injection timing overlaps with the fuel injection for the next cylinder, the control device retards the post-injection timing so that the post-injection does not overlap with the fuel injection for the next cylinder. If the post-injection timing is retarded so that the exhaust gas temperature does not exceed a predetermined temperature, the post-injection timing may overlap with the fuel injection for the next cylinder. In this case, the control device retards the post-injection timing so that the post-injection is performed after the fuel injection for the next cylinder is completed so that the post-injection does not overlap with the fuel injection for the next cylinder. In this way, by retarding the post-injection timing so that it does not overlap with the fuel injection for the next cylinder, it is possible to prevent two injectors from opening at the same time.

[0012] (2) Preferably, in the above (1), the multi-cylinder compression ignition internal combustion engine includes a filter that collects particulate matter contained in the exhaust gas. The control device may perform regeneration control to combust and remove the particulate matter collected in the filter, and may perform post injection while the regeneration control is being performed.

[0013] This configuration makes it possible to suppress an excessive rise in exhaust gas temperature, and to prevent the exhaust system components (particularly the exhaust manifold) from exceeding their designed heat resistance temperature, while using post injection to control filter regeneration.

[0014] (3) Preferably, in the above (1) or (2), the control device may estimate the cetane number of the injected fuel based on the exhaust gas temperature when the post injection is being performed, and set the post injection timing based on the cetane number.

[0015] For a given post-injection timing, the higher the cetane number, the more fuel is burned in the cylinder, resulting in a higher exhaust gas temperature. Therefore, it is possible to estimate the cetane number of the injected fuel based on the exhaust gas temperature when post-injection is being performed. With this configuration, the cetane number of the injected fuel is estimated based on the exhaust gas temperature when post-injection is being performed, and the post-injection timing can be set based on the estimated cetane number so that the exhaust gas temperature does not exceed a predetermined temperature.

[0016] (4) Preferably, the multi-cylinder compression ignition internal combustion engine in (2) above further includes a variable nozzle turbo provided in the exhaust passage upstream of the filter, and an intake air amount control means for controlling the intake air amount. The control device may control the intake air amount to a set value while the regeneration control is being executed, estimate the cetane number of the injected fuel based on the control amount of the intake air amount control means while the regeneration control is being executed, and set the post-injection timing based on the cetane number.

[0017] During filter regeneration control, the intake air amount control means controls the intake air amount to a set value to reduce the intake air amount (exhaust gas amount) in order to maintain a high filter temperature. For a given post-injection timing, the higher the cetane number, the more fuel is burned in the cylinder, raising the exhaust gas temperature. This increases the exhaust energy flowing into the variable nozzle turbocharger, increasing the boost pressure and therefore the intake air amount. Therefore, the higher the cetane number of the injected fuel, the larger the control amount during regeneration control, so the intake air amount control means can estimate the cetane number based on the control amount. With this configuration, the control device estimates the cetane number of the injected fuel based on the control amount of the intake air amount control means during regeneration control that performs post-injection, and can set the post-injection timing based on the estimated cetane number so that the exhaust gas temperature does not exceed a predetermined temperature.

[0018] (5) Preferably, in any of the above (1) to (4), the post injection is a multi-stage post injection in which injection is divided into multiple times, and the control device sets the post injection timing of each stage of the multi-stage post injection, and if any of the post injection timings of each stage overlaps with the fuel injection of the next cylinder, the control device may retard the post injection timing of each stage that overlaps with the fuel injection so that the post injection timing of each stage that overlaps with the fuel injection is after the main injection of the next cylinder.

[0019] With this configuration, multi-stage post injection is performed in which fuel is injected in multiple separate injections, thereby reducing the amount of post injection per injection and the penetration of the fuel spray. This prevents fuel from adhering to the cylinder wall (combustion chamber wall) and reduces oil dilution. If any of the post injection timings for each stage overlaps with the fuel injection for the next cylinder, the control device retards the post injection timing for each stage that overlaps with the fuel injection so that the post injection timing for each stage that overlaps with the fuel injection is after the main injection for the next cylinder. This allows the number of post injection divisions to be maintained, and the post injection timing for each stage that does not overlap with the fuel injection for the next cylinder is not retarded after the main injection for the next cylinder, allowing the post injection to be completed early.

[0020] (6) Preferably, in any of (1) to (4) above, the post injection is a multi-stage post injection in which injection is divided into multiple times, and the control device sets the post injection timing for each stage of the multi-stage post injection, and if any of the post injection timings for each stage overlaps with the fuel injection for the next cylinder, the control device may retard the post injection timing for each stage so that all of the post injection timings for each stage are after the main injection for the next cylinder.

[0021] With this configuration, multi-stage post injection is performed in which the fuel is injected in multiple separate injections, which reduces the amount of post injection per injection and the penetration force of the fuel spray. This prevents fuel from adhering to the cylinder wall (combustion chamber wall) and reduces oil dilution. If any of the post injection timings for each stage overlap with the fuel injection for the next cylinder, the control device retards the post injection timing for all stages so that they occur after the main injection for the next cylinder. This ensures the number of post injection divisions and reduces the penetration force of the fuel spray.

[0022] (7) Preferably, in any one of the above (1) to (6), the exhaust gas temperature may be the exhaust gas temperature in the exhaust manifold.

[0023] According to this configuration, the exhaust gas temperature is the exhaust gas temperature in the exhaust manifold, so that the temperature of the exhaust manifold can be prevented from exceeding the designed heat resistance temperature.

[0024] (8) A control method for a multi-cylinder compression ignition internal combustion engine disclosed herein is a control method for a multi-cylinder compression ignition internal combustion engine equipped with a filter in an exhaust passage that traps particulate matter contained in exhaust gas. The control method includes: performing a post-injection that injects fuel during an expansion stroke while performing regeneration control that burns and removes the particulate matter trapped in the filter; acquiring an exhaust gas temperature during the regeneration control; setting the post-injection timing so that the exhaust gas temperature does not exceed a predetermined temperature; and, if the post-injection timing overlaps with fuel injection for a subsequent cylinder, retarding the post-injection timing so that the post-injection does not overlap with fuel injection for the subsequent cylinder.

[0025] According to this method, while regeneration control is being executed to burn and remove particulate matter trapped in the filter, post-injection is performed in which fuel is injected during the expansion stroke, and the particulate matter trapped in the filter is burned and removed using the post-injection.

[0026] When post-injection is performed, in which fuel is injected during the expansion stroke, if the fuel has a high cetane number and is easily self-ignited, the post-injected fuel is more likely to burn in the cylinder, resulting in a higher exhaust gas temperature. Retarding the post-injection timing makes it more difficult for the fuel to burn in the cylinder. According to this method, the post-injection timing is set so that the exhaust gas temperature does not exceed a predetermined temperature. Because the post-injection timing is set to the retarded side so that the exhaust gas temperature does not exceed the predetermined temperature, even if the fuel has a high cetane number, the post-injected fuel can be prevented from burning in the cylinder, thereby preventing an excessive rise in the exhaust gas temperature.

[0027] According to this method, if the post-injection timing overlaps with the fuel injection of the next cylinder, the post-injection timing is retarded so that the post-injection does not overlap with the fuel injection of the next cylinder.Since the post-injection timing is retarded so that the post-injection is performed after the fuel injection of the next cylinder is completed so that the post-injection does not overlap with the fuel injection of the next cylinder, it is possible to avoid opening the valves of two injectors at the same time.

[0028] (9) In (8) above, if the post-injection timing overlaps with the fuel injection of the next cylinder, the post-injection timing may be retarded so that the post-injection timing comes after the main injection of the next cylinder.

[0029] According to this method, the crank angle from the main injection to the post injection of the next cylinder is relatively large, so that the post injection of the cylinder in question does not overlap with the fuel injection of the next cylinder.

[0030] (10) In the above (8) or (9), the exhaust gas temperature may be the exhaust gas temperature in the exhaust manifold.

[0031] According to this method, the exhaust gas temperature is the exhaust gas temperature in the exhaust manifold, so that the temperature of the exhaust manifold can be prevented from exceeding the designed heat resistance temperature. [Effects of the Invention]

[0032] According to the present disclosure, in a multi-cylinder compression ignition internal combustion engine, it is possible to prevent two injectors from opening simultaneously during post injection. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a schematic configuration diagram of a control device for a multi-cylinder compression ignition internal combustion engine according to an embodiment of the present invention. [Figure 2] 10A and 10B are diagrams illustrating overlapping of post-injection timing and fuel injection of the next cylinder. [Figure 3] 10A and 10B are diagrams illustrating the retardation of the post-injection timing in the present embodiment. [Figure 4] 4 is a flowchart showing an example of a fuel injection control process executed in an engine ECU. [Figure 5] 10 is a flowchart showing the details of S4. [Figure 6] 10 is a flowchart showing an example of a fuel injection control process executed by an engine ECU in the second embodiment. [Figure 7] 10 is a flowchart showing details of S400. [Figure 8] 4 is a flowchart showing an example of a process for controlling the intake air amount executed by the engine ECU. [Figure 9] 10 is a flowchart showing an example of a fuel injection control process executed by an engine ECU in a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0035] (Embodiment 1) FIG. 1 is a schematic diagram of a control device for a multi-cylinder compression ignition internal combustion engine according to this embodiment. Engine 1 is a multi-cylinder compression ignition internal combustion engine (diesel engine) equipped with a control device (engine ECU (Electronic Control Unit)) 100. In this embodiment, engine 1 is used as a drive source for a vehicle and is mounted on the vehicle. Engine 1 is an internal combustion engine that performs compression autoignition by injecting fuel from fuel injection valves (injectors) 14 into combustion chambers formed in cylinders 12 of an engine body 10. In this embodiment, engine 1 is a four-cylinder compression ignition internal combustion engine and includes four cylinders 12, numbered first (#1) to number four (#4). An injector 14 is provided for each cylinder 12.

[0036] An air cleaner 22, an intercooler 24, and a throttle valve (diesel throttle valve) 26 are provided in the intake passage 20 of the engine 1. Fresh air, from which foreign matter has been removed by the air cleaner 22, is supercharged (compressed) by a compressor 32 of a turbocharger 30, cooled by the intercooler 24, supplied to an intake manifold 28, and then supplied to each combustion chamber through an intake port.

[0037] Exhaust gases discharged from the combustion chambers are collected in an exhaust manifold 50 and released into the outside air via an exhaust passage 52. A portion of the exhaust gases is returned to the intake manifold 28 via an EGR (Exhaust Gas Recirculation) passage 60. An EGR cooler 62 and an EGR valve 64 are provided in the EGR passage 60.

[0038] The exhaust passage 52 is provided with, from the upstream side, the turbine 34 of the turbocharger 30, a small oxidation catalyst (ATC: After Turbo Catalyst) 70, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 71, and a DPF (Diesel Particulate Filter) 72. The DPF 72 is a filter that collects particulate matter (PM) in the exhaust gas and purifies the exhaust by appropriately burning and removing the collected PM. Although not shown, a urea addition valve and a selective reduction catalyst may be provided downstream of the DPF 72. Note that a NOx storage-reduction catalyst (NSR (NOx Storage-Reduction) catalyst) may be provided instead of or in addition to the urea addition valve and the selective reduction catalyst.

[0039] In this embodiment, the turbocharger 30 is a variable nozzle turbo, and by controlling the opening of a variable nozzle (variable vane) 341 provided in the housing of the turbine 34, the exhaust gas passage area in the housing can be changed and the supercharging efficiency can be adjusted.

[0040] Fuel is stored in a fuel tank 40. The fuel in the fuel tank 40 is supplied to a high-pressure fuel pump 42 by a feed pump 41, and the high-pressure fuel discharged from the high-pressure fuel pump 42 is pressure-fed to a common rail 44 via a fuel passage 43. The high-pressure fuel stored in the common rail 44 is injected from the injector 14 into the combustion chamber (into the cylinder).

[0041] In this embodiment, the injector 14 is a piezoelectric injector. A piezoelectric injector utilizes the expansion and contraction caused by the inverse piezoelectric effect of a piezoelectric element as an actuator. The injector 14 is driven by a drive circuit 200 to open and close a fuel injection hole (not shown). When no current is supplied from the drive circuit 200 to the injector 14 (when no voltage is applied to the piezoelectric element), the fuel injection hole is closed. When a current is supplied from the drive circuit 200 to the injector 14 (when a voltage is applied to the piezoelectric element), the fuel injection hole is opened and fuel is injected into a combustion chamber formed in the cylinder 12.

[0042] Drive circuit 200 includes a DC / DC converter (not shown) that boosts the power supplied from battery 300. The voltage boosted by the DC / DC converter is applied to a capacitor (not shown), which stores electric charge to be supplied to injectors 14 (piezo elements). The electric charge stored in the capacitor is selectively supplied to each injector 14, causing each injector 14 to inject fuel.

[0043] The engine ECU 100, which is a control device, includes a CPU 101, a memory 102 consisting of ROM and RAM, an input / output port (not shown) for inputting and outputting various signals, and executes predetermined calculations based on information stored in the memory 102 and information from various sensors, thereby controlling the injector 14, the throttle valve 26, the high-pressure fuel pump 42, the variable nozzle 341, etc.

[0044] The various sensors that input signals to the engine ECU 100 include, for example, a crank angle sensor 111, an engine rotation speed sensor 112, an accelerator pedal sensor 113, an air flow meter 114, an exhaust temperature sensor 115, a pressure sensor 116, a vehicle speed sensor 117, and the like.

[0045] The crank angle sensor 111 detects the crank angle CA of the engine 1. The engine rotation speed sensor 112 detects the rotation speed NE of the engine 1. The accelerator pedal sensor 113 detects the amount of accelerator pedal operation (hereinafter also referred to as "accelerator opening") AP by the user. The air flow meter 114 detects the amount of intake air Ga of the engine 1.

[0046] The exhaust temperature sensor 115 is provided in the exhaust manifold 50 and detects the exhaust gas temperature Tex inside the exhaust manifold 50. The pressure sensor 116 detects the pressure difference (front-to-rear pressure difference) ΔP inside the exhaust passage 52 between the upstream (inlet) and downstream (outlet) of the DPF 72. The vehicle speed sensor 117 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted.

[0047] In the engine 1 configured as described above, the engine ECU 100 executes fuel injection control, intake air amount control, DPF regeneration control, and the like. For example, in fuel injection control, the engine ECU 100 calculates the total fuel injection amount Qa from a fuel injection amount map based on the accelerator opening AP and the engine rotation speed NE. The engine ECU 100 calculates the pilot injection amount Qi, pre-injection amount Qr, and after-injection amount Qt from the relationship between the engine rotation speed NE, the total fuel injection amount Qa, the ignition delay of the main injection, the in-cylinder pressure, and the like. The engine ECU 100 then calculates the main injection amount Qm by subtracting the pilot injection amount Qi, pre-injection amount Qr, and after-injection amount Qt from the total fuel injection amount Qa.

[0048] Furthermore, the engine ECU 100 calculates the main injection timing Itm from an injection timing map based on the engine rotation speed NE and the total fuel injection amount Qa (or the accelerator pedal position AP). Then, the pilot injection timing Iti, the pre-injection timing Itr, and the after-injection timing Itt are set based on the main injection timing Itm from the relationship between the engine rotation speed NE, the total fuel injection amount Qa, the ignition delay of the main injection, the in-cylinder pressure, and the like. Note that the engine ECU 100 may calculate each injection timing It* from each injection timing map based on the engine rotation speed NE and the total fuel injection amount Qa (or the accelerator pedal position AP). When the crank angle of the engine 1 reaches each injection timing It*, the engine ECU 100 controls (opens the valve) the injector 14 using the drive circuit 200 to inject fuel of the pilot injection amount Qi, the pre-injection amount Qr, the main injection amount Qm, and the after-injection amount Qt.

[0049] In engine 1, PM contained in exhaust gas emitted from engine 1 is trapped by DPF 72. When the amount of PM accumulated in DPF 72 reaches or exceeds a predetermined value, engine ECU 100 executes regeneration control to regenerate DPF 72 by raising the temperature of DPF 72 and burning off the accumulated PM. For example, engine ECU 100 calculates the amount of PM Gpm emitted from engine 1 using a PM calculation map based on engine speed NE and total fuel injection amount Qa (or accelerator opening AP), and then integrates the calculated PM amount Gpm to obtain an integrated value ΣGpm. Then, when integrated value ΣGpm reaches or exceeds a predetermined value, or when differential pressure ΔP across the engine 1 detected by pressure sensor 116 reaches or exceeds a set value, engine ECU 100 executes regeneration control of DPF 72. When regeneration control is performed, the opening degree TA of the throttle valve 26 and the opening degree VA of the variable nozzle 341 are controlled so that the intake air amount per rotation (Ga / N) becomes a set value in order to raise the temperature of the DPF 72, and post-injection is performed to inject fuel during the expansion stroke. The throttle valve 26 and the variable nozzle 341 correspond to an example of the "air amount control means" of this disclosure. The regeneration control of the DPF 72 ends when the accumulated PM is burned and removed, and the amount of accumulated PM becomes equal to or less than the set value.

[0050] The post-injection amount QPs, which is the amount of fuel injected in the post-injection, may be a predetermined amount, or may be calculated from a post-injection amount map based on the engine rotation speed NE and the total fuel injection amount Qa. In this embodiment, multi-stage post-injection is performed in which the post-injection is divided into four injections, and one-fourth of the post-injection amount QPs is injected in each post-injection.

[0051] FIG. 2 is a diagram illustrating the overlap of post-injection timing and fuel injection into the next cylinder. In this embodiment, the ignition order of the engine 1 is the first cylinder (#1) → the third cylinder (#3) → the fourth cylinder (#4) → the second cylinder (#2). FIG. 2 shows fuel injection (valve opening of the injector 14) into the first cylinder (#1) and the next cylinder (the cylinder in which fuel injection occurs next after the first cylinder (#1)), the third cylinder (#3), and the horizontal axis represents the crank angle CA. The crank angle CA is set to 0° CA when the first cylinder (#1) is at top dead center (TDC) on the compression side.

[0052] As shown in Figure 2, the main injection for the first cylinder (#1) is performed immediately after the TDC on the compression side of the first cylinder (#1). The pilot injection and pre-injection for the first cylinder (#1) are performed before top dead center, which is advanced from the main injection, and the after-injection is performed on the retard side immediately after the main injection. In this embodiment, when diesel fuel with a standard cetane number is used as the fuel, the post-injection timing is set after top dead center (ATDC), during the expansion stroke at around 90° CA, and multiple post-injections are performed.

[0053] When a fuel with a high cetane number, such as HVO, is used in the engine 1, there is a concern that the post-injected fuel will burn in the combustion chamber, causing the exhaust gas temperature Tex to rise excessively and exceed the design heat resistance temperature of the exhaust manifold 50. Therefore, when a fuel with a high cetane number, such as HVO, is used, it is possible to retard the post-injection timing so that the exhaust gas temperature Tex does not exceed a predetermined temperature. However, if the post-injection timing is retarded, as shown by the dashed line in Figure 2, the fuel injection (pilot injection, pre-injection, or main injection) for the next cylinder, No. 3 cylinder (#3), and the post-injection timing (post injection) for No. 1 cylinder (#1) may overlap (overlap), as shown by the dashed line in Figure 2.

[0054] When the post-injection timing of the first cylinder (#1) and the fuel injection timing of the third cylinder (#3) overlap, the injector 14 of the first cylinder (#1) and the injector 14 of the third cylinder (#3) are required to open simultaneously (to inject fuel simultaneously). When driving the two injectors 14 to open simultaneously, there is a concern that the power of the drive circuit 200 may be insufficient. For example, the capacitor of the drive circuit 200 may not be able to charge in time, and the injector 14 may not be able to be driven properly.

[0055] In this embodiment, for example, when a fuel with a high cetane number is used and the post-injection timing is retarded so that the exhaust gas temperature Tex does not exceed a predetermined temperature, if the post-injection timing overlaps with the fuel injection of the next cylinder, as shown by the dashed line in Figure 2, the post-injection timing is further retarded so that the post-injection does not overlap with the fuel injection of the next cylinder.

[0056] FIG. 3 is a diagram illustrating the retardation of the post-injection timing in this embodiment. In this embodiment, multi-stage post-injection is performed in which post-injection is divided into four injections. FIG. 3A shows an example in which, when a portion of the post-injection timing of each stage (each stage post-injection timing) overlaps with the fuel injection of the next cylinder, the post-injection timing of each stage that overlaps with the fuel injection of the next cylinder is retarded. Referring to FIG. 3A, when the post-injection timing of the first cylinder (#1) is retarded so that the exhaust gas temperature Tex does not exceed a predetermined temperature, if a portion of the post-injection timing of each stage overlaps with the fuel injection of the third cylinder (#3), as shown by the dashed line, the overlapping post-injection timing of each stage is retarded so that it is after the main injection of the third cylinder (#3). In the example shown in FIG. 3A, the third and fourth stages of the post-injection timing of each stage of the first cylinder (#1) overlap with the pilot injection of the third cylinder (#3). As shown by the solid lines, the third and fourth stages of the overlapping post-injection timing are retarded so that they occur after the main injection of the third cylinder (#3) (the exhaust stroke of the first cylinder (#1)). As a result, the post-injection timing of the first cylinder (#1) is retarded so that the post-injection of the first cylinder (#1) does not overlap with the fuel injection of the next cylinder, the third cylinder (#3).

[0057] FIG. 3B shows an example in which all post-injection timings for each stage are retarded when a portion of the post-injection timing overlaps with the fuel injection of the next cylinder. Referring to FIG. 3B, when the post-injection timing for the first cylinder (#1) is retarded so that the exhaust gas temperature Tex does not exceed a predetermined temperature, if a portion of the post-injection timing overlaps with the fuel injection of the third cylinder (#3), as shown by the dashed line, all multi-stage post-injection timings are retarded so that they occur after the main injection of the third cylinder (#3). In the example shown in FIG. 3B, the third and fourth stages of the post-injection timing for the first cylinder (#1) overlap with the pilot injection of the third cylinder (#3). As shown by the solid line, all post-injection timings for each stage (the post-injection timings for the first through fourth stages) are retarded so that they occur after the main injection of the third cylinder (#3) (the exhaust stroke of the first cylinder (#1)). As a result, the post-injection timing of the first cylinder (#1) is retarded so that the post-injection of the first cylinder (#1) does not overlap with the fuel injection of the next cylinder, the third cylinder (#3).

[0058] 4 is a flowchart showing an example of a fuel injection control process executed by engine ECU 100. This flowchart is executed for each cylinder and is repeatedly processed every 720° CA. In step (hereinafter, step will be abbreviated as "S") 1, each injection amount Q* and each injection timing It* are calculated based on the engine rotation speed NE, accelerator pedal position AP, etc. Each injection amount Q* is a pilot injection amount Qi, a pre-injection amount Qr, a main injection amount Qm, and an after-injection amount Qt, and as described above, the total fuel injection amount Qa is calculated from an injection amount calculation map based on the engine rotation speed NE and the accelerator pedal position AP, and each injection amount Q* is calculated. Each injection timing It* is a pilot injection timing Iti, a pre-injection timing Itr, a main injection timing Itm, and an after-injection timing Itt, and as described above, the calculation method is described above.

[0059] In the next step S2, it is determined whether or not regeneration control is being performed for the DPF 72. If regeneration control for the DPF 72 is not being performed, a negative determination is made and the process proceeds to step S3. If regeneration control for the DPF 72 is being performed, a positive determination is made and the process proceeds to step S4.

[0060] In S3, flag F is set to 0, and then the process proceeds to S5. In S4, the post injection amount QPs and the post injection timing Itps are calculated. Details of S4 (method of calculating the post injection amount QPs and the post injection timing Itps) will be described later. After S4, the process proceeds to S5.

[0061] In S5, when each injection timing arrives, the injector 14 is driven (valve opened) to inject the respective injection amount of fuel. If S4 is processed, post-injection is performed, and if S4 is not processed, post-injection is not performed.

[0062] 5 is a flowchart showing the details of S4. If the determination in S2 is affirmative, the exhaust gas temperature Tex is detected by the exhaust gas temperature sensor 115 in S10.

[0063] In subsequent S11, it is determined whether the exhaust gas temperature Tex is equal to or higher than a predetermined temperature A. The predetermined temperature A is, for example, a temperature sufficiently lower than the designed heat-resistant temperature of the exhaust manifold 50, and is a preset value. If the exhaust gas temperature Tex is lower than the predetermined temperature A (Tex < A), a negative determination is made and the process proceeds to S12. If the exhaust gas temperature Tex is equal to or higher than the predetermined temperature A (Tex ≥ A), an affirmative determination is made and the process proceeds to S14.

[0064] In S12, it is determined whether the flag F is 1. The flag F is set to 1 in S17 described later. If S17 has not been processed, the flag F is 0, a negative determination is made, and the process proceeds to S13. If S17 has already been processed and the flag F is 1, an affirmative determination is made and the process proceeds to S19.

[0065] In S13, the cetane number Cn is set to a reference value. The reference value may be the cetane number of standard light oil (reference cetane number). When S13 is processed, the process proceeds to S19.

[0066] In S14, it is determined whether the flag F is 1. If the flag F is 0, a negative determination is made and the process proceeds to S15. If the flag F is 1, an affirmative determination is made and the process proceeds to S22.

[0067] In S15, the reference ekimani temperature Ts is calculated. The reference ekimani temperature Ts is the temperature indicated by the exhaust gas temperature of the exhaust manifold 50 when fuel with the reference cetane number is used, the post-injection timing is calculated using the reference cetane number, and post-injection is performed. The reference ekimani temperature Ts is stored in advance as a two-dimensional map with the engine rotation speed NE and the total fuel injection amount Qa as parameters through experiments or the like. In S15, based on the engine rotation speed NE detected by the engine rotation speed sensor 112 and the total fuel injection amount Qa calculated in S1, the reference ekimani temperature Ts is calculated from the two-dimensional map.

[0068] In S16, the cetane number Cn (of the fuel currently being used) is calculated based on the exhaust gas temperature Tex and the reference exhaust manifold temperature Ts. For example, the cetane number Cn is estimated based on the difference between the exhaust gas temperature Tex and the reference exhaust manifold temperature Ts. The higher the exhaust gas temperature Tex is than the reference exhaust manifold temperature Ts, and the greater the difference, the higher the calculated cetane number Cn. The cetane number Cn calculated in S16 is a value higher than the reference cetane number. In the following S17, flag F is set to 1, and then the process proceeds to S19.

[0069] In S19, a post injection amount QPs is calculated based on the total fuel injection amount Qa and the engine rotation speed NE. The post injection amount QPs may be a predetermined amount (constant amount). In this embodiment, multi-stage post injection is performed in which post injection is divided into four injections, so 1 / 4 of the post injection amount QPs is calculated as the post injection amount for each stage.

[0070] In S19, the post-injection timing Itps is calculated based on the total fuel injection amount Qa, the engine rotation speed NE, and the cetane number Cn. For example, the first-stage post-injection timing (reference post-injection timing) Itpm-1 when fuel with a reference cetane number is used is stored in a post-injection timing map with the total fuel injection amount Qa and the engine rotation speed NE as parameters. This post-injection timing map is set in advance through experiments or the like and stored in memory 102. The reference post-injection timing Itpm-1 is calculated from the post-injection timing map based on the total fuel injection amount Qa and the engine rotation speed NE. The reference post-injection timing Itpm-1 calculated from the post-injection timing map is corrected to the retard side based on the cetane number Cn. For example, the retard amount r is calculated based on the cetane number Cn. The retard amount r is set to 0 when the cetane number Cn is the reference cetane number and to increase as the cetane number Cn increases. The retard amount r is set in advance through experiments, etc., so that when post-injection is performed using fuel with a cetane number Cn, the post-injected fuel does not burn in the cylinder (combustion chamber). Once the retard amount r is calculated based on the cetane number Cn, the injection timing retarded by the retard amount r from the standard post-injection timing Itpm-1 is set as the new standard post-injection timing Itpm-1.

[0071] In S19, once the reference post-injection timing (first-stage post-injection timing) Itpm-1 is calculated, the second-stage post-injection timing Itpm-2, the third-stage post-injection timing Itpm-3, and the fourth-stage post-injection timing Itpm-4 are set. In this disclosure, the post-injection timing Itps is a general term for the first-stage to fourth-stage post-injection timings (each-stage post-injection timing) Itpm1 to 4. The second-stage to fourth-stage post-injection timings Itpm-2 to Itpm-4 are set, for example, based on the post-injection amount QPs and the engine speed NE. During each stage post-injection, the valve-opening time of the injector 14 is set to a time required to inject a fuel amount equal to ¼ of the post-injection amount QPs. The injection crank angle Fca corresponding to the set valve-opening time is calculated based on the engine speed NE. The second-stage post-injection timing Itpm-2 is set to a crank angle retarded by "injection crank angle Fca+m" from the reference post-injection timing (first-stage post-injection timing) Itpma-1. "m" is a value that is set based on the responsiveness of the injector 14, etc. The third-stage post-injection timing Itpm-3 is set to a crank angle that is retarded by "injection crank angle Fca+m" from the second-stage post-injection timing Itpm-2. The fourth-stage post-injection timing Itpm-4 is set to a crank angle that is retarded by "injection crank angle Fca+m" from the third-stage post-injection timing Itpm-3.

[0072] In the next S20, it is determined whether the post-injection timing Itps overlaps with the fuel injection of the next cylinder. Specifically, it is determined whether any of the first-stage post-injection timing Itpm-1 to the fourth-stage post-injection timing ITpm-4 overlaps with the pilot injection of the next cylinder. The crank angle at which the pilot injection of the next cylinder is performed may be, for example, calculated during the previous fuel injection control process for the next cylinder, or may be calculated during the current fuel injection control process for the next cylinder. If any of the first-stage post-injection timing Itpm-1 to the fourth-stage post-injection timing ITpm-4 overlaps with the pilot injection of the next cylinder (if it overlaps with the crank angle at which the pilot injection of the next cylinder is performed), a positive determination is made and the process proceeds to S21. If all of the post-injection timings Itpm-1 to ITpm-4 are advanced relative to the pilot injection of the next cylinder and do not overlap with the pilot injection of the next cylinder, a negative determination is made and the process proceeds to S5 (see FIG. 4).

[0073] In S21, the post-injection timing Itps is retarded to a crank angle after the main injection so that the post-injection does not overlap with the fuel injection of the next cylinder. Specifically, as described with reference to FIG. 3A, if any of the first-stage post-injection timing Itpm-1 through the fourth-stage post-injection timing Itpm-4 overlaps with the pilot injection of the next cylinder, the post-injection timing of each subsequent stage after the overlap with the pilot injection of the next cylinder may be retarded to a crank angle after the main injection of the next cylinder. If the third-stage post-injection timing Itpm-3 overlaps with the pilot injection of the next cylinder, the third-stage post-injection timing Itpm-3 and the fourth-stage post-injection timing Itpm-4 are retarded to a crank angle after the main injection of the next cylinder. For example, the third-stage post-injection timing Itpm-3 may be set to a crank angle that is retarded by a predetermined crank angle n from the end timing of the main injection of the next cylinder, and the fourth-stage post-injection timing Itpm-4 may be set to a crank angle that is retarded by "injection crank angle Fca+m" from the third-stage post-injection timing Itpm-3.

[0074] Alternatively, as explained with reference to FIG. 3B, if any of the first-stage post-injection timing Itpm-1 through the fourth-stage post-injection timing Itpm-4 overlaps with the pilot injection of the next cylinder, all of the post-injection timings for each stage may be retarded to a crank angle after the main injection of the next cylinder. For example, if the third-stage post-injection timing Itpm-3 overlaps with the pilot injection of the next cylinder, all of the first-stage post-injection timings Itpm-1 through Itpm-4 are retarded to a crank angle after the main injection of the next cylinder. For example, the reference post-injection timing (first-stage post-injection timing) Itpm-1 is set to a crank angle retarded by a predetermined crank angle n from the end of the main injection of the next cylinder. Then, the second-stage and subsequent post-injection timings Itpm-2 through Itpm-4 are sequentially set to crank angles retarded by the "injection crank angle Fca+m." After S21, the process proceeds to S5 (see FIG. 4).

[0075] In S22, the cetane number Cn is corrected to an increased value, and then the process proceeds to S19. When a positive determination is made in S14 and the process proceeds to S22, flag F is set to 1. Flag F is set to 1 (S17) when the cetane number Cn is calculated based on the exhaust gas temperature Tex and the reference exhaust manifold temperature Ts (when S16 is processed). Then, in S19, the post-injection timing Itps is corrected (set) to the retard side based on the cetane number Cn, and post injection is performed based on the corrected post-injection timing Itps. When the post-injection timing Itps is corrected (set) to the retard side, the exhaust gas temperature Tex decreases compared to before the correction and becomes lower than the predetermined temperature A. As a result, a negative determination is made in S11 and the process proceeds to S12.

[0076] However, if the cetane number Cn calculated in S16 is calculated to be lower than the cetane number of the fuel being used for some reason (for example, when the operating state of the engine 1 is transient), the retard amount based on the cetane number Cn will be small, and there is a possibility that the exhaust gas temperature Tex will become equal to or higher than the predetermined temperature A. For this reason, if the exhaust gas temperature Tex becomes equal to or higher than the predetermined temperature A even when the post-injection timing Itps is corrected to be retarded based on the cetane number Cn calculated in S16, the cetane number Cn is corrected to be increased in S22, thereby increasing the retard amount of the post-injection timing Itps and preventing the exhaust gas temperature Tex from rising excessively.

[0077] (Embodiment 2) FIG. 6 is a flowchart showing an example of fuel injection control processing executed by engine ECU 100 in the second embodiment. In the second embodiment, the configuration of engine 1, intake air amount control, DPF regeneration control, etc. are the same as those in the first embodiment. The flowchart in FIG. 6 is also executed for each cylinder and is repeatedly processed every 720° CA. In the flowchart in FIG. 6, the processing of S1, S2, and S5 is the same as that in the flowchart in FIG. 4, and therefore description thereof will be omitted. In the flowchart in FIG. 6, S3 and S4 in the flowchart in FIG. 4 are changed to S300 and S400.

[0078] In S300, the flag F is set to 1 and the retard amount R is set to 0, and then the process proceeds to S5.

[0079] 7 is a flowchart showing the details of S400. If a positive determination is made in S2, the post-injection timing Itps is calculated in S41 based on the total fuel injection amount Qa and the engine rotation speed NE. For example, the first-stage post-injection timing (reference post-injection timing) Itpm-1 is stored in a post-injection timing map using the total fuel injection amount Qa and the engine rotation speed NE as parameters. This post-injection timing map is set in advance through experiments using fuel with a reference cetane number, and is stored in memory 102. The reference post-injection timing Itpm-1 is obtained from the post-injection timing map based on the total fuel injection amount Qa and the engine rotation speed NE.

[0080] In S41, when the reference post injection timing (the first-stage post injection timing) Itpm-1 is calculated, the second-stage post injection timing Itpm-2, the third-stage post injection timing Itpm-3, and the fourth-stage post injection timing Itpm-4 are set. The post injection timings Itpm-2 to 4 from the second stage to the fourth stage are, for example, calculated based on the post injection amount QPs and the engine rotational speed NE in the same manner as in the first embodiment (see S19 in FIG. 5), and the injection crank angle Fca corresponding to the valve opening time of the injector 14 is calculated to set the post injection timing Itps for each stage.

[0081] In S42, the exhaust gas temperature Tex is detected. The exhaust gas temperature Tex is detected from the exhaust temperature sensor 115.

[0082] In the subsequent S43, it is determined whether the exhaust gas temperature Tex is equal to or higher than a predetermined temperature B. The predetermined temperature B is, for example, a temperature sufficiently lower than the designed heat-resistant temperature of the exhaust manifold 50 and is a preset value. The predetermined temperature B may be the same value as the predetermined temperature A. If the exhaust gas temperature Tex is lower than the predetermined temperature B (Tex < B), a negative determination is made and the process proceeds to S48. If the exhaust gas temperature Tex is equal to or higher than the predetermined temperature B (Tex ≥ B), an affirmative determination is made and the process proceeds to S44.

[0083] In S44, it is determined whether the flag F is 1. The flag F is set to 1 in S45. If the flag F is 0, a negative determination is made and the process proceeds to S45. If the flag F is 1, an affirmative determination is made and the process proceeds to S46.

[0084] In step 45, the flag F is set to 1, and after setting the retard amount R to α, the process proceeds to S47. α is the magnitude such that the exhaust gas temperature Tex significantly decreases when the post injection timing Itps is set to the retard side by the retard amount R = α, and is set in advance by experiments or the like.

[0085] In S47, the post-injection timing Itps is retarded. Specifically, each of the first to fourth stage post-injection timings Itpm-1 to Itpm-4 calculated in S41 is corrected to the retard side by the retard amount R, and new first to fourth stage post-injection timings Itpm-1 to Itpm-4 are set. Then, the process proceeds to S48.

[0086] In S48, it is determined whether the post-injection timing Itps overlaps with the fuel injection of the next cylinder. This process is the same as S20 (FIG. 5), so its description will be omitted. If the determination in S48 is affirmative, the process proceeds to S49. If the determination in S48 is negative, the process proceeds to S5 (see FIG. 6).

[0087] In S49, the post-injection timing Itps is retarded to a crank angle after the main injection so that the post-injection does not overlap with the fuel injection of the next cylinder. As in S21 (FIG. 5), if any of the first-stage post-injection timing Itpm-1 to the fourth-stage post-injection timing Itpm-4 overlaps with the pilot injection of the next cylinder, as explained in FIG. 3(A), the post-injection timing of each stage after the overlap with the pilot injection of the next cylinder may be retarded to a crank angle after the main injection of the next cylinder. Alternatively, as in S21, as explained in FIG. 3(B), if any of the first-stage post-injection timing Itpm-1 to the fourth-stage post-injection timing Itpm-4 overlaps with the pilot injection of the next cylinder, the post-injection timing of all stages may be retarded to a crank angle after the main injection of the next cylinder. After S49, the process proceeds to S5 (see FIG. 6).

[0088] In S46, the retard amount R is corrected to increase, and then the program proceeds to S47. When a positive determination is made in S44 and the program proceeds to S46, S45 is processed and flag F is set to 1. In S45, flag F is set to 1, and retard amount R is set to α. Then, in S47, the post-injection timing Itps is corrected to the retard side by the retard amount R, and post injection is performed based on the corrected post-injection timing Itps. When the post-injection timing Itps is corrected (set) to the retard side, the exhaust gas temperature Tex decreases compared to before the correction, and becomes lower than the predetermined temperature B. As a result, a negative determination is made in S43 and the program proceeds to S48.

[0089] However, even with the retard amount R (=α) calculated in S45, there is a possibility that the exhaust gas temperature Tex may become equal to or higher than the predetermined temperature B for some reason (for example, during a transition in the operating state of the engine 1). For this reason, if the exhaust gas temperature Tex becomes equal to or higher than the predetermined temperature B even when the post-injection timing Itps is corrected to the retard side based on the retard amount R calculated in S45, the retard amount R is increased in S46 to increase the retard amount of the post-injection timing Itps, thereby preventing the exhaust gas temperature Tex from rising excessively.

[0090] (Variation) In the above embodiments (Embodiments 1 and 2), in order to raise the temperature of the DPF 72 when regeneration control of the DPF 72 is being executed, the opening TA of the throttle valve 26 and the opening VA of the variable nozzle 341 are controlled so that the intake air amount per revolution (Ga / N) becomes a set value, and post-injection is performed to inject fuel during the expansion stroke. Then, the exhaust gas temperature Tex is detected, and the post-injection timing Itps is retarded so that the exhaust gas temperature Tex does not exceed a predetermined temperature when using an HVO or the like with a high cetane number.

[0091] In the modified example, the cetane number Cn of the fuel being used is estimated based on the control amount of the opening TA of the throttle valve 26 and the control amount of the opening VA of the variable nozzle 341 during regeneration control, and the post-injection timing Itps is set using the estimated cetane number Cn.

[0092] 8 is a flowchart showing an example of intake air amount control processing executed by the engine ECU 100. This flowchart is repeatedly executed at predetermined intervals while the engine 1 is operating. In S7, it is determined whether or not regeneration control of the EPF 72 is underway. If regeneration control is not underway, a negative determination is made and the process proceeds to S8. If regeneration control is underway, a positive determination is made and the process proceeds to S9.

[0093] In S8, the opening degree TA of the throttle valve 26 and the opening degree VA of the variable nozzle 341 are normally controlled. In normal control, for example, the opening degree TA is controlled based on the accelerator opening degree AP and the engine rotation speed NE. Furthermore, the opening degree VA is controlled so as to reach a target boost pressure set based on the accelerator opening degree AP and the engine rotation speed NE.

[0094] In S9, the openings TA and VA are controlled so that the intake air amount per revolution (Ga / N) becomes a set value C. The set value C may be a constant value and is set in advance by experiments or the like. Then, a throttle valve opening map during regeneration and a boost pressure map during regeneration are set using the total fuel injection amount Qa and the engine rotation speed NE as parameters so that the intake air amount (Ga / N) becomes the set value C, and are stored in memory 102. The throttle valve opening map during regeneration and the boost pressure map during regeneration are set by experiments or the like using fuel with a reference cetane number.

[0095] In S9, a target throttle valve opening degree TAt is calculated from a throttle valve opening degree map during regeneration based on the total fuel injection amount Qa and the engine rotation speed NE, and a target boost pressure Pt is calculated from a boost pressure map during regeneration. The engine ECU 100 controls the opening degree VA of the variable nozzle 341 so that the opening degree TA of the throttle valve 26 becomes the target throttle valve opening degree TAt and so that the boost pressure becomes the target boost pressure Pt. The intake air amount per revolution (Ga / N) is calculated from the intake air amount Ga detected by the air flow meter 114 and the engine rotation speed NE detected by the engine rotation speed sensor 112. Then, a deviation Δ between the calculated intake air amount (Ga / N) and a set value C is calculated. A correction control amount VAh for the opening degree VA is calculated so that this deviation Δ becomes zero, and the opening degree VA, which is controlled to the target boost pressure, is corrected and controlled. Furthermore, if the deviation Δ does not become 0 even when the correction control amount of the opening VA becomes equal to or greater than a predetermined value, a correction control amount TAh of the opening TA of the throttle valve 26 is calculated so that the deviation Δ becomes 0, and the opening TA is corrected and controlled. The correction control amount VAh of the opening VA is set to a positive value as a control amount in the direction in which the opening VA increases. The correction control amount TAh of the opening TA is set to a positive value as a control amount in the direction in which the opening TA decreases. The correction control amount VAh of the opening VA or the correction control amount TAh of the opening TA corresponds to an example of the "control amount of the intake air amount control means" of the present disclosure.

[0096] Fig. 9 is a flowchart showing an example of fuel injection control processing executed by engine ECU 100 in a modified example. In the fuel injection control of the modified example, among S1 to S5 in the flowchart (Fig. 4) of the first embodiment, S4 is changed to S4A. Therefore, Fig. 9 omits S1 to S3 and S5 and shows the details of S4A.

[0097] 9, in S60, the correction control amount VAh of the opening VA and the correction control amount TAh of the opening TA are obtained. The correction control amount VAh and the correction control amount VAh are values ​​calculated in S9 (FIG. 8).

[0098] In S61, it is determined whether the control amount As is equal to or greater than a predetermined value β. The control amount As is a value obtained by adding the corrected control amount VAh and the corrected control amount TAh. During regeneration control of the DPF 72, the intake air amount (Ga / N) is controlled to a set value C in order to raise the temperature of the DPF 72. When the post-injection timing Itps is the same, the higher the cetane number, the more fuel is burned in the cylinder, causing the exhaust gas temperature to rise, which in turn increases the exhaust energy flowing into the turbocharger 30 and the boost pressure, thereby increasing the intake air amount (Ga / N). Therefore, the higher the cetane number of the injected fuel, the larger the corrected control amount VAh of the opening degree VA and the larger the corrected control amount TAh of the opening degree TA. Therefore, it is possible to estimate the cetane number based on the control amount As.

[0099] The predetermined value β is the maximum value of the control variable As that is assumed when fuel with a standard cetane number is used and the standard cetane number is used to calculate the post-injection timing Itps and perform post-injection, and is set in advance by experiment, etc. If the control variable As is smaller than the predetermined value β (As<β), a negative determination is made and the process proceeds to S62. If the control variable As is equal to or greater than the predetermined value β (As≧β), a positive determination is made and the process proceeds to S64.

[0100] In S62, it is determined whether flag F is 1. Flag F is set to 1 in S66, which will be described later. If S66 has not been processed, flag F is 0, a negative determination is made, and the process proceeds to S63. If S66 has already been processed and flag F is 1, an affirmative determination is made, and the process proceeds to S67.

[0101] In S63, the cetane number Cn is set to a reference value. The reference value may be the cetane number of standard diesel fuel (reference cetane number). After S63 is completed, the process proceeds to S67.

[0102] In S64, it is determined whether or not flag F is 1. If flag F is 0, a negative determination is made and the process proceeds to S65. If flag F is 1, an affirmative determination is made and the process proceeds to S70.

[0103] In S65, the cetane number Cn is calculated based on the controlled variable As. The larger the controlled variable As, the higher the calculated cetane number Cn. The relationship between the controlled variable As and the cetane number Cn may be determined in advance by experiment or the like and stored in the memory 102. The cetane number Cn calculated in S65 is a value higher than the reference cetane number. In the following S66, the flag F is set to 1, and then the process proceeds to S67.

[0104] In S67, a post injection amount QPs is calculated based on the total fuel injection amount Qa and the engine rotation speed NE. In addition, a post injection timing Itps is calculated based on the total fuel injection amount Qa, the engine rotation speed NE, and the cetane number Cn. The calculation method of the post injection amount QPs and the post injection timing Itps in S67 is the same as that in S19 (FIG. 5), so a description thereof will be omitted.

[0105] In the next step S68, it is determined whether the post-injection timing Itps coincides with the fuel injection of the next cylinder. The process of S68 is the same as that of S20 (FIG. 5), and therefore a description thereof will be omitted.

[0106] In S69, the post-injection timing Itps is retarded to the crank angle after the main injection so that the post-injection does not overlap with the fuel injection of the next cylinder. The processing of S69 is the same as S21 (Fig. 1), so a description thereof will be omitted.

[0107] In S70, the cetane number Cn is corrected to increase, and then the process proceeds to S67. When a positive determination is made in S64 and the process proceeds to S70, flag F is set to 1. Flag F is set to 1 when the cetane number Cn is calculated based on the controlled variable As (when S65 is processed). Then, in S67, the post-injection timing Itps is corrected (set) to the retard side based on the cetane number Cn, and post-injection is performed at the corrected post-injection timing Itps. When the post-injection timing Itps is corrected (set) to the retard side, less fuel is burned in the cylinder, the exhaust gas temperature Tex falls, the exhaust energy flowing into the turbocharger 30 decreases, and the boost pressure falls. As a result, the intake air amount (Ga / N) decreases, and the controlled variable As becomes smaller, so a negative determination is made in S61 and the process proceeds to S62.

[0108] However, if the cetane number Cn calculated in S65 is lower than the cetane number of the fuel being used for some reason (for example, when the operating state of the engine 1 is transitional), the retard amount based on the cetane number Cn will be small, the exhaust gas temperature Tex will not decrease, and there is a possibility that the exhaust energy flowing into the turbocharger 30 will not be reduced. For this reason, if the exhaust gas temperature Tex does not decrease and the exhaust energy does not decrease even when the post injection timing Itps is retarded based on the cetane number Cn calculated in S65, the cetane number Cn is increased in S70 to increase the retard amount of the post injection timing Itps and prevent the exhaust gas temperature Tex from rising excessively.

[0109] According to the above embodiment, the engine ECU 100 of the engine 1 executes post-injection, which injects fuel during the expansion stroke, and sets the post-injection timing Itps so that the exhaust gas temperature Tex does not exceed a predetermined temperature (S19, S47, S67). As a result, the post-injection timing Itps is set to the retarded side so that the exhaust gas temperature Tex does not exceed the predetermined temperature, so that even if the fuel has a high cetane number, the post-injected fuel can be prevented from burning in the cylinder, and an excessive rise in the exhaust gas temperature Tex can be suppressed.

[0110] If the post-injection timing Itps is set to the retarded side so that the exhaust gas temperature Tex does not exceed a predetermined temperature, the post-injection timing Itps may overlap with the fuel injection of the next cylinder. If the post-injection timing Itps overlaps with the fuel injection of the next cylinder (positive determinations in S20, S48, and S68), the engine ECU 100 retards the post-injection timing Itps so that the post-injection does not overlap with the fuel injection of the next cylinder (S21, S49, S69). By retarding the post-injection timing Itps so that it does not overlap with the fuel injection of the next cylinder, it is possible to prevent the two injectors 14 from opening simultaneously.

[0111] According to the above embodiment, the engine 1 is equipped with the DPF 72 that traps particulate matter contained in the exhaust gas. The engine ECU 100 executes regeneration control to combust and remove the particulate matter trapped in the DPF 72, and executes post-injection while the regeneration control is being executed. This makes it possible to perform regeneration control of the DPF 72 using post-injection while suppressing an excessive rise in the exhaust gas temperature Tex and preventing the temperature from exceeding the design heat resistance temperature of exhaust system components (particularly the exhaust manifold 50).

[0112] According to the above embodiment, the post injection is a multi-stage post injection in which fuel is injected in multiple divided injections. The engine ECU 100 sets the post injection timings Itpm-1 to Itpm-4 for each stage of the multi-stage post injection, and when any of the post injection timings Itpm-1 to Itpm-4 overlaps with the fuel injection of the next cylinder, the engine ECU 100 retards the post injection timings Itpm-1 to Itpm-4 that overlap with the fuel injection so that the post injection timings Itpm-1 to Itpm-4 that overlap with the fuel injection are after the main injection of the next cylinder.

[0113] By performing multi-stage post injection, the amount of post injection per injection can be reduced and the penetration of the fuel spray can be reduced, which prevents fuel from adhering to the cylinder wall (combustion chamber wall) and reduces oil dilution. If any of the post injection timings Itpm-1 to 4 overlaps with the fuel injection of the next cylinder, the post injection timings Itpm-1 to 4 that overlap with the fuel injection are retarded so that they are after the main injection of the next cylinder. This ensures the number of post injection divisions, and because the post injection timings Itpm-1 to 4 that do not overlap with the fuel injection are not retarded after the main injection of the next cylinder, the post injection can be completed early.

[0114] Furthermore, when any of the post-injection timings Itpm-1 to Itpm-4 overlaps with the fuel injection of the next cylinder, the engine ECU 100 may retard the post-injection timings Itpm-1 to Itpm-4 so that all of the post-injection timings Itpm-1 to Itpm-4 occur after the main injection of the next cylinder. This ensures the number of divided post-injections and reduces the penetration of the fuel spray.

[0115] In the above embodiment, post-injection is performed during regeneration control of the DPF 72. However, post-injection is not limited to being performed during regeneration control of the DPF 72, and may be performed, for example, during warm-up (temperature increase) of the ATC 70 or the DCO 71. The number of divided post-injections is not limited to four, and the post-injection does not have to be multi-stage post-injection.

[0116] In the above embodiment, during regeneration control of the DPF 72, the opening degree TA of the throttle valve 26 and the opening degree VA of the variable nozzle 341 are controlled so that the intake air amount (Ga / N) becomes the set value C. However, it is also possible to control either the opening degree TA or the opening degree VA so that the intake air amount (Ga / N) becomes the set value C.

[0117] In the above embodiment, the engine 1 has been described as performing pilot injection, pre-injection, main injection, and after-injection as fuel injection. However, the fuel injection mode is not limited to this. For example, pre-injection and after-injection may be omitted. Furthermore, the pilot injection may be a multi-stage injection. Furthermore, any method may be used to calculate each fuel injection amount. For example, the main injection amount Qm may be calculated from the accelerator opening AP and the engine rotation speed NE, and other injection amounts such as the pilot injection amount Qi may be calculated based on the main injection amount Qm.

[0118] The above embodiment has been described using a four-cylinder engine 1. The engine 1 does not have to be a four-cylinder engine as long as it has multiple cylinders.

[0119] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0120] 1 engine, 10 engine body, 12 cylinder, 14 fuel injection valve (injector), 20 intake passage, 22 air cleaner, 24 intercooler, 26 throttle valve (diesel throttle valve), 28 intake manifold, 30 turbocharger, 32 compressor, 34 turbine, 341 variable nozzle, 40 fuel tank, 41 feed pump, 42 high-pressure fuel pump, 43 fuel passage, 44 common rail, 50 exhaust manifold, 52 exhaust passage, 60 ERG passage, 62 EGR cooler, 64 EGR valve, 70 ATC, 71 DOC, 72 DPF, 100 engine ECU, 101 CPU, 102 memory, 111 crank angle sensor, 112 engine rotation speed sensor, 113 accelerator pedal sensor, 114 air flow meter, 115 exhaust temperature sensor, 116 Pressure sensor, 117 Vehicle speed sensor, 200 Drive circuit, 300 Battery.

Claims

1. A control device for a multi-cylinder compression ignition internal combustion engine, The control device Fuel is injected during the expansion stroke, and post-injection is performed. Set the post-injection timing so that the exhaust gas temperature does not exceed a specified temperature. A control device for a multi-cylinder compression ignition internal combustion engine, wherein if the post-injection timing overlaps with fuel injection of a subsequent cylinder, the control device retards the post-injection timing so that the post-injection does not overlap with fuel injection of the subsequent cylinder.

2. The multi-cylinder compression ignition internal combustion engine is provided with a filter that collects particulate matter contained in exhaust gas, The control device performing regeneration control to combust and remove the particulate matter trapped in the filter; 2. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 1, wherein the post injection is performed while the regeneration control is being performed.

3. The control device estimating the cetane number of the injected fuel based on the exhaust gas temperature when the post injection is being performed; 3. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 1, wherein the post-injection timing is set based on the cetane number.

4. The multi-cylinder compression ignition internal combustion engine includes: a variable nozzle turbo provided in an exhaust passage upstream of the filter; and an intake air amount control means for controlling the intake air amount, The control device During execution of the regeneration control, the intake air amount is controlled to a set value, estimating the cetane number of the injected fuel based on the control amount of the intake air amount control means during execution of the regeneration control; 3. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 2, wherein the post-injection timing is set based on the cetane number.

5. The post-injection is a multi-stage post-injection in which fuel is injected in multiple separate injections, The control device setting a post-injection timing for each stage of the multi-stage post-injection; 3. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 1, wherein, when any of the post-injection timings of each stage overlaps with the fuel injection of the next cylinder, the post-injection timing of each stage that overlaps with the fuel injection is retarded so that the post-injection timing of each stage that overlaps with the fuel injection is after the main injection of the next cylinder.

6. The post-injection is a multi-stage post-injection in which fuel is injected in multiple separate injections, The control device setting a post-injection timing for each stage of the multi-stage post-injection; 3. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 1, wherein, when any of the post-injection timings of each stage overlaps with the fuel injection of the next cylinder, the post-injection timings of each stage are retarded so that all of the post-injection timings of each stage are after the main injection of the next cylinder.

7. 3. The control device for a multi-cylinder compression ignition internal combustion engine according to claim 1, wherein the exhaust gas temperature is the exhaust gas temperature in an exhaust manifold.

8. A control method for a multi-cylinder compression ignition internal combustion engine equipped with a filter in an exhaust passage that captures particulate matter contained in exhaust gas, comprising: performing post-injection, which is fuel injection during an expansion stroke while performing regeneration control to combust and remove the particulate matter trapped in the filter; acquiring an exhaust gas temperature during the regeneration control; setting a post-injection timing so that the exhaust gas temperature does not exceed a predetermined temperature; If the post-injection timing overlaps with the fuel injection of a subsequent cylinder, retarding the post-injection timing so that the post-injection does not overlap with the fuel injection of the subsequent cylinder.

9. 9. The control method for a multi-cylinder compression ignition internal combustion engine according to claim 8, wherein, when the post-injection timing overlaps with the fuel injection of the subsequent cylinder, the post-injection timing is retarded so that the post-injection timing is after the main injection of the subsequent cylinder.

10. 10. The control method for a multi-cylinder compression ignition internal combustion engine according to claim 8, wherein the exhaust gas temperature is the exhaust gas temperature in an exhaust manifold.

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