Engine Control Unit

Abstract

To improve heat efficiency of an engine.SOLUTION: An engine control device 100 includes: an engine having an injector 13 for injecting a fuel to a combustion chamber and an ignition plug 14 for igniting an air-fuel mixture; and a control portion 50 for controlling the injector and the ignition plug to change combustion modes according to a required torque. The combustion modes include: spark ignition combustion with ignition of a gasoline fuel: first premixed compression ignition combustion not with ignition of modified fuel obtained by modifying a part of the gasoline fuel to peroxide; second premixed compression ignition combustion with ignition of the modified fuel; and diffusion combustion not with the ignition of the modified fuel. The control portion 50 controls the injector and the ignition plug to perform the second premixed compression ignition combustion when the required torque is less than a first prescribed value, to perform the first premixed compression ignition combustion when the required torque is the first prescribed value or more and less than a second prescribed value, to perform the spark ignition combustion when the required torque is the second prescribed value or more and less than the third prescribed value, and to perform the diffusion combustion when the required torque is the third prescribed value or more.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an engine control device. [Background technology]

[0002] Conventionally, there is known a device that reforms gasoline fuel supplied to an engine (see, for example, Patent Document 1). In the device described in Patent Document 1, gasoline fuel with an octane number for a spark ignition engine is reformed as necessary into low-octane gasoline with high ignition properties through an oxidation reaction in an on-board reformer, and then the gasoline is injected into the combustion chamber, where it is compressed and ignited (diffusion combustion). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-112891 A Summary of the Invention [Problem to be solved by the invention]

[0004] The device described in Patent Document 1 assumes only diffusion combustion using highly ignitable reformed fuel. However, since there are operating ranges in which the thermal efficiency of the engine is higher when unreformed gasoline fuel is used as is, the device described in Patent Document 1 may result in a decrease in the thermal efficiency of the engine. [Means for solving the problem]

[0005] An engine control device according to one aspect of the present invention includes an engine having an injector that injects fuel into a combustion chamber and an ignition plug that ignites a mixture of fuel and air in the combustion chamber, and a control unit that controls the injector and the ignition plug so as to switch the combustion mode according to the required torque of the engine. The combustion modes include spark ignition combustion accompanied by ignition of gasoline fuel, first homogeneous charge compression ignition combustion accompanied by ignition of reformed fuel obtained by reforming a part of the gasoline fuel into peroxide, second homogeneous charge compression ignition combustion accompanied by ignition of the reformed fuel, and diffusion combustion accompanied by ignition of the reformed fuel. The control unit controls the injector and the spark plug so as to switch the combustion type to second homogeneous charge compression ignition combustion when the required torque is less than a first predetermined value, to switch the combustion type to first homogeneous charge compression ignition combustion when the required torque is equal to or greater than the first predetermined value and less than a second predetermined value greater than the first predetermined value, to switch the combustion type to spark ignition combustion when the required torque is equal to or greater than the second predetermined value and less than a third predetermined value greater than the second predetermined value, and to switch the combustion type to diffusion combustion when the required torque is equal to or greater than the third predetermined value. Effect of the Invention

[0006] According to the present invention, the thermal efficiency of the engine can be improved. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram for explaining the thermal efficiency of an engine in spark ignition combustion. [Diagram 2] 1 is a diagram showing an example of an internal configuration of an engine of an engine control device according to an embodiment of the present invention; [Diagram 3] FIG. 2 is a diagram illustrating an example of a fuel supply passage that supplies fuel to an engine of the engine control device according to the embodiment of the present invention. [Figure 4] 1 is a block diagram showing an example of a configuration of a main part of an engine control device according to an embodiment of the present invention; [Diagram 5] FIG. 2 is a diagram for explaining the relationship between the peroxide concentration in a fuel and the octane number and ignition quality. [Figure 6]FIG. 2 is a diagram for explaining a combustion mode that improves the thermal efficiency of the engine. [Figure 7] 5 is a flowchart showing an example of a combustion mode switching process executed by the ECU of FIG. 4; [Figure 8] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from spark ignition combustion to homogeneous charge compression ignition combustion. [Figure 9] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from homogeneous charge compression ignition combustion to spark ignition combustion. [Figure 10] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from homogeneous charge compression ignition combustion to spark ignition assisted homogeneous charge compression ignition combustion. [Figure 11] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from spark ignition assisted homogeneous charge compression ignition combustion to homogeneous charge compression ignition combustion. [Figure 12] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from spark ignition combustion to diffusion combustion. [Figure 13] 5 is a flowchart showing an example of a process executed by the ECU of FIG. 4 when switching from diffusion combustion to spark ignition combustion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 13. An engine control device according to an embodiment of the present invention is mounted on a vehicle and applied to an engine having an injector that injects fuel into a combustion chamber and an ignition plug that ignites a mixer in the combustion chamber, and performs engine control to improve thermal efficiency over the entire operating range.

[0009] FIG. 1 is a diagram for explaining the thermal efficiency of an engine with spark ignition (SI) combustion. As shown in FIG. 1, when SI combustion is performed, in the low load region where the required torque of the engine is small, the required intake amount is small, so the throttle opening becomes small, which increases pumping loss during intake and reduces thermal efficiency. On the other hand, in homogenous charge compression ignition (HCCI) combustion, the output torque is adjusted by the fuel injection amount, so the throttle opening is maintained near full open even in the low load region, and there is no reduction in thermal efficiency due to pumping loss.

[0010] When SI combustion with ignition is performed, in the high load range where the required torque of the engine is large, the ignition timing must be retarded from the optimal ignition timing (target ignition timing) in order to suppress knocking, in which the mixture self-ignites near the wall of the cylinder 2 before the flame propagates, resulting in reduced thermal efficiency. On the other hand, when diffusion combustion without ignition is performed, the fuel evaporates and mixes with the air before burning, so such a problem does not occur.

[0011] Therefore, in this embodiment, the engine control device is configured as follows so that the thermal efficiency can be improved over the entire operating range of the engine by switching the combustion mode according to the required torque.

[0012] Fig. 2 is a diagram showing a schematic diagram of an example of an internal configuration of an engine 1 of an engine control device (hereinafter, device) 100 according to an embodiment of the present invention. As shown in Fig. 2, the engine 1 has a cylinder block 3 in which a cylinder 2 is formed, and a cylinder head 4 covering an upper part of the cylinder block 3. The cylinder head 4 is provided with an intake port 5 through which intake air to the engine 1 passes, and an exhaust port 6 through which exhaust air from the engine 1 passes. The intake port 5 is provided with an intake valve 7 that opens and closes the intake port 5, and the exhaust port 6 is provided with an exhaust valve 8 that opens and closes the exhaust port 6. The intake valve 7 and the exhaust valve 8 are driven to open and close by a valve mechanism (not shown).

[0013] A piston 9 is disposed in each cylinder 2 so as to be slidable within the cylinder 2, and a combustion chamber 10 is formed facing the piston 9. A throttle valve 12 is provided in an intake passage 11 which communicates with the combustion chamber 10 via an intake port 5. The throttle valve 12 is formed of, for example, a butterfly valve, and adjusts the amount of air (intake amount) drawn into the combustion chamber 10. The opening of the throttle valve 12 (throttle opening) is controlled by an electronic control unit (ECU (Electronic Control Unit)) 50 (FIG. 4).

[0014] An injector 13 and a spark plug 14 are attached to the cylinder head 4 so that they each face the combustion chamber 10. The injector 13 is configured as a direct-injection type fuel injection valve, and injects fuel into the combustion chamber 10. The spark plug 14 generates a spark using electrical energy, and ignites the mixture of fuel and air in the combustion chamber 10. The fuel injection timing (valve opening timing) and fuel injection amount (valve opening time) of the injector 13, the ignition timing of the spark plug 14, and the on / off of ignition by the spark plug 14 are controlled by the ECU 50 (FIG. 4).

[0015] When the intake port 5 is opened, the exhaust port 6 is closed, and the piston 9 moves down, air (fresh air) is drawn into the combustion chamber 10 through the intake port 5 (intake stroke). When the intake port 5 and the exhaust port 6 are closed and the piston 9 moves up, the air or air-fuel mixture in the combustion chamber 10 is compressed, and the pressure in the combustion chamber 10 gradually increases (compression stroke).

[0016] When SI combustion is performed, fuel is injected into the combustion chamber 10 from an injector 13 during the intake stroke or compression stroke, and the mixture is ignited by a spark plug 14 near the compression top dead center (TDC), and the fuel in the combustion chamber 10 is burned by flame propagation. In SI combustion, gasoline fuel is used.

[0017] When HCCI combustion is performed, fuel is injected from the injector 13 into the combustion chamber 10 during the intake stroke or compression stroke, and when the temperature of the mixture in the combustion chamber 10 rises due to compression, the fuel burns by self-ignition near the compression top dead center (TDC). In HCCI combustion, gasoline fuel can be used in a region where the required torque of the engine is relatively large and combustion is stable. When HCCI combustion is performed in a region where the required torque of the engine is relatively small and combustion is unstable, it is necessary to use a fuel that is more ignitable than gasoline fuel.

[0018] When HCCI combustion is performed in a range where the required torque of the engine is even smaller, in addition to using fuel with high ignition properties, it is necessary to ignite the mixture with a spark plug 14 near the top dead center (TDC) of the compression stroke to assist ignition. This type of combustion is hereinafter referred to as spark assisted homogeneous charge compression ignition (SAHCCI) combustion. In SAHCCI combustion, part of the fuel in the combustion chamber 10 is burned by flame propagation, and the remaining fuel is burned by self-ignition in the combustion chamber 10 which has become hot due to the combustion.

[0019] In the case of diffusion combustion, when fuel is injected from the injector 13 into the combustion chamber 10, the fuel evaporates and mixes with air, and is burned. In the diffusion combustion, it is necessary to use a fuel that is highly ignitable.

[0020] When fuel is burned in the combustion chamber 10, the pressure in the combustion chamber 10 rises suddenly, and the piston 9 moves down (expansion stroke). The intake port 5 is closed, the exhaust port 6 is opened, and the piston 9 moves up, and the air (exhaust) in the combustion chamber 10 is discharged from the exhaust port 6 (exhaust stroke). The piston 9 reciprocates along the inner wall of the cylinder 2, causing the crankshaft 16 to rotate via the connecting rod 15.

[0021] A crank angle sensor 17 is provided on the crankshaft 16 of the engine 1 to detect a rotation angle (crank angle) θ of the crankshaft 16. A signal indicating the detection result by the crank angle sensor 17 is transmitted to the ECU 50 (FIG. 4). Although not shown, the engine 1 is also provided with a knock sensor 18 (FIG. 4) attached to the cylinder block 3 to detect an amplitude value K of vibration of the engine 1. A signal indicating the detection result by the knock sensor 18 is transmitted to the ECU 50 (FIG. 4). Instead of the knock sensor 18, an internal cylinder pressure sensor may be provided to detect a pressure (internal cylinder pressure) P in the combustion chamber 10. In this case, a fluctuation dP / dθ of the internal cylinder pressure P with respect to a change in the crank angle θ is calculated, and the amplitude value K of the vibration of the engine 1 can be calculated based on the fluctuation dP / dθ of the internal cylinder pressure P.

[0022] Gasoline fuel, which is mainly composed of hydrocarbons, can be oxidized and reformed using a catalyst such as N-hydroxyphthalimide (NHPI) to generate peroxides, which can improve its ignition ability. Specifically, NHPI easily extracts hydrogen atoms with oxygen molecules to generate phthalimide-N-oxyl (PINO) radicals. The PINO radical extracts hydrogen atoms from the hydrocarbons (RH) contained in the fuel to generate alkyl radicals (R·). The alkyl radicals combine with oxygen molecules to generate alkylperoxy radicals (ROO·). The alkylperoxy radicals extract hydrogen atoms from the hydrocarbons contained in the fuel to generate alkylhydroperoxides (ROOH), which are peroxides, such as cumene hydroperoxide. [ka]

[0023] As the oxidation reaction progresses, the peroxide concentration increases, and as the oxidation reaction progresses further, the peroxides are decomposed into oxidants such as alcohols, aldehydes, and ketones, decreasing the peroxide concentration while increasing the oxidant concentration. In order to increase the peroxide concentration in the fuel and improve the ignition ability of the fuel, it is necessary to adjust the progress of the oxidation reaction to within an appropriate range. Specifically, it is necessary to adjust the peroxide concentration in the reformed fuel to a predetermined concentration or higher so that the octane number of the reformed fuel obtained by oxidatively reforming a portion of the gasoline fuel is a predetermined value or lower.

[0024] Fig. 3 is a diagram showing a schematic example of a fuel supply passage 20 that supplies fuel to the engine 1 of the device 100. As shown in Fig. 3, the fuel supply passage 20 is provided with a fuel tank 21 that stores gasoline fuel, a reformer 22 that oxidizes and reforms the gasoline fuel, a reformed fuel tank 23 that stores the reformed fuel, and a mixer 24 that mixes the gasoline fuel and the reformed fuel. The mixed fuel mixed by the mixer 24 is injected into the combustion chamber 10 of the engine 1 via the injector 13 (Fig. 2).

[0025] The liquid phase of the fuel tank 21 and the inlet of the reformer 22 are connected via a pipe 25, and gasoline fuel stored in the fuel tank 21 is supplied to the reformer 22 via the pipe 25 by an electric pump 26 provided in the pipe 25. The operation of the electric pump 26 is controlled by the ECU 50 (FIG. 4).

[0026] The reformer 22 is filled with a catalyst such as NHPI. The reformer 22 is provided with a heater 27 that adjusts the temperature of the reformer 22, and oxidizes and reforms a part of the gasoline fuel supplied from the fuel tank 21 into peroxides at a reforming rate according to the temperature. The reformed fuel after oxidative reforming contains peroxides such as cumene hydroperoxide at a rate according to the reforming rate. The operation of the heater 27 is controlled by the ECU 50 (FIG. 4).

[0027] The outlet of the reformer 22 and the reformed fuel tank 23 are connected via a pipe 28. The reformed fuel reformed in the reformer 22 is supplied to the reformed fuel tank 23 via the pipe 28. A condenser 29 is provided in the pipe 28 between the reformer 22 and the reformed fuel tank 23. The gaseous fuel after reforming is condensed in the condenser 29 and stored as a liquid in the reformed fuel tank 23. The reformed fuel tank 23 is provided with a concentration sensor 23a, for example of a capacitance type, which detects the peroxide concentration C1 of the reformed fuel stored as a liquid in the reformed fuel tank 23. A signal indicating the detection result by the concentration sensor 23a is transmitted to the ECU 50 (FIG. 4).

[0028] The liquid phase of the fuel tank 21 is further connected to the mixer 24 via a pipe 30. The gasoline fuel stored in the fuel tank 21 is supplied to the mixer 24 via the pipe 30 by an electric pump 31 provided in the pipe 30. The liquid phase of the reformed fuel tank 23 is connected to the mixer 24 via a pipe 32. The reformed fuel stored in the reformed fuel tank 23 is supplied to the mixer 24 via the pipe 32 by an electric pump 33 provided in the pipe 32. The operation of the electric pumps 31 and 33 is controlled by the ECU 50 (FIG. 4). The mixer 24 is provided with, for example, a capacitance-type concentration sensor 24a, which detects the peroxide concentration C2 of the mixed fuel. A signal indicating the detection result by the concentration sensor 24a is transmitted to the ECU 50 (FIG. 4). If the engine 1 has an in-cylinder pressure sensor, the ignition quality of the fuel supplied to the engine 1 may be estimated based on the in-cylinder pressure P, and the peroxide concentration C2 in the fuel may be estimated based on the ignition quality of the fuel. In this case, the concentration sensor 24a may be omitted.

[0029] Fig. 4 is a block diagram showing a schematic example of a configuration of a main part of the device 100. As shown in Fig. 4, the device 100 is mainly composed of an ECU 50, which includes a computer having a processing unit 51 such as a CPU, a storage unit 52 such as a ROM, a RAM, and other peripheral circuits (not shown) such as an I / O interface. The ECU 50 may be configured as a part of an engine control ECU that controls the operation of the engine 1.

[0030] The crank angle sensor 17, the knock sensor 18, and the concentration sensors 23a and 24a are electrically connected to the ECU 50, and signals from each of the sensors are input to the ECU 50. The ECU 50 is also electrically connected to actuators for the throttle valve 12, the injector 13, the spark plug 14, the electric pumps 26, 31, and 33, and the heater 27, and sends control signals from the ECU 50 to each actuator.

[0031] The ECU 50 controls the opening of the throttle valve 12, the fuel injection timing and fuel injection amount of the injector 13, the ignition timing of the spark plug 14, and the on / off of ignition by the spark plug 14, etc., according to the operating conditions of the engine 1, such as the engine speed and required torque. The target opening of the throttle valve 12, the target fuel injection timing and target fuel injection amount of the injector 13, the target ignition timing of the spark plug 14, etc. are determined in advance according to the operating conditions of the engine 1, and are stored in the storage unit 52 of the ECU 50 as a characteristic map or the like. The ECU 50 also controls the electric pump 26 and the heater 27 so that the peroxide concentration C1 of the reformed fuel detected by the concentration sensor 23a is equal to or higher than a predetermined concentration corresponding to a predetermined octane number. As a result, the reformed fuel tank 23 stores reformed fuel whose peroxide concentration C1 is equal to or higher than a predetermined concentration and whose octane number is equal to or lower than a predetermined value.

[0032] Fig. 5 is a diagram for explaining the relationship between the peroxide concentration C2 and the octane number and ignition quality in the fuel supplied to the engine 1. As shown in Fig. 5, the higher the peroxide concentration C2, the lower the octane number and the higher the ignition quality.

[0033] FIG. 6 is a diagram for explaining a combustion mode for improving the thermal efficiency of the engine 1, and shows an example of a characteristic map that is preset and stored in the storage unit 52 of the ECU 50. As shown in FIG. 6, from the viewpoint of improving the thermal efficiency of the engine 1, when the required torque is less than the first predetermined value Te1, SAHCCI combustion is performed; when it is equal to or greater than the first predetermined value Te1 and less than the second predetermined value Te2, HCCI combustion is performed; when it is equal to or greater than the second predetermined value Te2 and less than the third predetermined value Te3, SI combustion is performed; and when it is equal to or greater than the third predetermined value Te3, diffusion combustion is preferably performed (Te1 < Te2 < Te3). The first predetermined value Te1, the second predetermined value Te2, and the third predetermined value Te3 are preset according to the operating conditions of the engine 1 such as the engine speed and the required torque, and are stored in the storage unit 52 of the ECU 50 as, for example, a characteristic map.

[0034] The ECU 50 (processing unit 51) refers to the characteristic map stored in the storage unit 52, identifies an optimal combustion mode according to the required torque of the engine 1, and controls the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the ignition plug 14 so as to switch the combustion mode as necessary. More specifically, when performing combustion with gasoline fuel, the electric pump 33 is turned off and the electric pump 31 is turned on to directly guide the gasoline fuel stored in the fuel tank 21 to the injector 13. When performing combustion with reformed fuel, the electric pump 31 is turned off and the electric pump 33 is turned on to guide the reformed fuel stored in the reformed fuel tank 23 to the injector 13. At this time, when the remaining amount of the reformed fuel stored in the reformed fuel tank 23 is insufficient, in addition to the electric pump 33, the electric pump 31 may also be turned on to guide a mixed fuel of gasoline fuel and reformed fuel to the injector 13.

[0035] When performing SI combustion, the throttle valve 12, injector 13, and ignition plug 14 are controlled according to the target throttle opening map, target fuel injection timing map, target fuel injection amount map, and target ignition timing map for SI combustion stored in the storage unit 52. When performing HCCI combustion, the throttle valve 12 and injector 13 are controlled according to the target throttle opening map, target fuel injection timing map, and target fuel injection amount map for HCCI combustion stored in the storage unit 52, and the ignition by the ignition plug 14 is turned off. When performing SAHCCI combustion, the throttle valve 12, injector 13, and ignition plug 14 are controlled according to the target throttle opening map, target fuel injection timing map, target fuel injection amount map, and target ignition timing map for SAHCCI combustion stored in the storage unit 52. When performing diffusion combustion, the throttle valve 12 and injector 13 are controlled according to the target throttle opening map, target fuel injection timing map, and target fuel injection amount map for diffusion combustion stored in the storage unit 52, and the ignition by the ignition plug 14 is turned off.

[0036] In this way, by switching the combustion mode according to the required torque, the thermal efficiency can be improved throughout the operating range of the engine 1. At this time, in addition to gasoline fuel, by using reformed fuel, it is possible to switch not only to SI combustion and HCCI combustion in the medium load region, but also to HCCI combustion and SAHCCI combustion in the low load region and diffusion combustion in the high load region.

[0037] <Switching from SI Combustion to HCCI Combustion> When the required torque becomes less than the second predetermined value Te2 during the execution of SI combustion, the ECU 50 switches to HCCI combustion on the condition that the amplitude value K detected by the knock sensor 18 is less than the predetermined amplitude value Kα and the peroxide concentration C2 detected by the concentration sensor 24a is equal to or higher than the predetermined concentration Cα. The predetermined amplitude value Kα and the predetermined concentration Cα are preset according to the operating conditions of the engine 1 such as the engine speed and the required torque, and are stored in the storage unit 52 of the ECU 50 as a characteristic map, for example.

[0038] In addition, when the peroxide concentration C2 is less than the predetermined concentration Cα and the peroxide concentration in the reformed fuel to be switched is insufficient, the electric pump 26 and the heater 27 can be controlled to increase the peroxide concentration in the reformed fuel before performing the switching.

[0039] After switching to HCCI combustion, when the amplitude value K becomes less than the predetermined amplitude value Kα, the ECU 50 determines that the HCCI combustion is being stably performed. On the other hand, when the amplitude value K becomes greater than or equal to the predetermined amplitude value Kα, the reformed fuel is returned to gasoline fuel. In this case, the combustion shifts to HCCI combustion using gasoline fuel. If the amplitude value K is still greater than or equal to the predetermined amplitude value Kα after the transition to HCCI combustion using gasoline fuel, the combustion mode is returned to SI combustion and the SI combustion using gasoline fuel is resumed.

[0040] <Switching from HCCI Combustion to SI Combustion> During the execution of HCCI combustion, when the required torque becomes equal to or greater than the second predetermined value Te2, the ECU 50 switches to SI combustion on the condition that the amplitude value K is greater than or equal to the predetermined amplitude value Kα. After switching to SI combustion, when the amplitude value K becomes less than the predetermined amplitude value Kα, the ECU 50 determines that the SI combustion is being stably performed. On the other hand, when the amplitude value K becomes greater than or equal to the predetermined amplitude value Kα, the ignition plug 14 is controlled to retard the ignition timing. By retarding the ignition timing until the amplitude value K becomes less than the predetermined amplitude value Kα, the SI combustion can be stabilized.

[0041] <Switching from HCCI Combustion to SAHCCI Combustion> The ECU 50 calculates the crank angle acceleration d 2 θ / d 2 t based on the crank angle θ detected by the crank angle sensor 17. During the execution of HCCI combustion, when the required torque becomes less than the first predetermined value Te1, the ECU 50 calculates the crank angle acceleration d 2 θ / d 2Switching to SAHCCI combustion is performed under the conditions that t is equal to or greater than a predetermined angular velocity aα, the amplitude value K is less than a predetermined amplitude value Kβ, and the peroxide concentration C2 is equal to or greater than a predetermined concentration Cβ. The predetermined angular velocity aα, the predetermined amplitude value Kβ, and the predetermined concentration Cβ are set in advance according to the operating conditions of the engine 1, such as the engine speed and required torque, and are stored in the memory unit 52 of the ECU 50 as, for example, a characteristics map.

[0042] After switching to SAHCCI combustion, the ECU50 crank angle acceleration d 2 θ / d 2 When t is less than a predetermined angular velocity aα and the amplitude value K is less than a predetermined amplitude value Kβ, it is determined that SAHCCI combustion is stable. 2 θ / d 2 When t is equal to or greater than a predetermined angular velocity aα or the amplitude value K is equal to or greater than a predetermined amplitude value Kβ, the spark plug 14 is controlled to retard the ignition timing. 2 θ / d 2 By retarding the ignition timing until t is less than a predetermined angular velocity aα and the amplitude value K is less than a predetermined amplitude value Kβ, SAHCCI combustion can be stabilized.

[0043] When the ECU 50 does not switch from HCCI combustion to SAHCCI combustion, it continues HCCI combustion when the peroxide concentration C2 is equal to or greater than the predetermined concentration Cβ. On the other hand, when the peroxide concentration C2 is less than the predetermined concentration Cβ, it switches to SI combustion using gasoline fuel. After switching to SI combustion, the ECU 50 2 θ / d 2 When t is less than a predetermined angular velocity aα and the amplitude value K is less than a predetermined amplitude value Kβ, it is determined that SI combustion is being performed stably. 2 θ / d 2 When t is equal to or greater than a predetermined angular velocity aα or the amplitude value K is equal to or greater than a predetermined amplitude value Kβ, the spark plug 14 is controlled to retard the ignition timing. 2 θ / d 2 By retarding the ignition timing until t becomes less than a predetermined angular velocity aα and the amplitude value K becomes less than a predetermined amplitude value Kβ, it is possible to stabilize SI combustion.

[0044] <Switching from SAHCCI Combustion to HCCI Combustion> When the required torque becomes equal to or greater than the first predetermined value Te1 during the execution of SAHCCI combustion, the ECU 50 determines that the crank angle acceleration d 2 θ / d 2 t is less than the predetermined angular velocity aα, the amplitude value K is equal to or greater than the predetermined amplitude value Kβ, and the peroxide concentration C2 is equal to or greater than the predetermined concentration Cγ, and then switches to HCCI combustion. The predetermined concentration Cγ is preset according to the operating conditions of Engine 1 such as the engine speed and the required torque, and is stored in the storage unit 52 of the ECU 50 as a characteristic map, for example.

[0045] After switching to HCCI combustion, when the amplitude value K becomes less than the predetermined amplitude value Kβ, the ECU 50 determines that the HCCI combustion is being stably performed. On the other hand, when the amplitude value K becomes equal to or greater than the predetermined amplitude value Kβ, the injector 13 is controlled to inject gasoline fuel instead of the reformed fuel. By using gasoline fuel with a lower ignition property instead of the reformed fuel with a higher ignition property, the HCCI combustion can be stabilized.

[0046] <Switching from SI Combustion to Diffusion Combustion> When the required torque becomes equal to or greater than the third predetermined value Te3 during the execution of SI combustion, the ECU 50 switches to diffusion combustion on the condition that the amplitude value K is equal to or greater than the predetermined amplitude value Kγ. The predetermined amplitude value Kγ is preset according to the operating conditions of Engine 1 such as the engine speed and the required torque, and is stored in the storage unit 52 of the ECU 50 as a characteristic map, for example.

[0047] When the amplitude value K becomes less than the predetermined amplitude value Kε after switching to the diffusion combustion, the ECU 50 determines that the diffusion combustion is being performed stably. On the other hand, when the amplitude value K becomes equal to or greater than the predetermined amplitude value Kε, the ECU 50 controls the injector 13 to retard the fuel injection timing. By retarding the fuel injection timing until the amplitude value K becomes less than the predetermined amplitude value Kε, the diffusion combustion can be stabilized. The predetermined amplitude value Kε is set in advance according to the operating conditions of the engine 1, such as the engine speed and the required torque, and is stored in the storage unit 52 of the ECU 50 as, for example, a characteristic map.

[0048] <Switching from diffusion combustion to SI combustion> When the required torque becomes less than the third predetermined value Te3 during the diffusion combustion, the ECU 50 increases the crank angular acceleration d 2 θ / d 2 Switching to SI combustion is performed under the condition that t is equal to or greater than a predetermined angular velocity aβ and the amplitude value K is less than a predetermined amplitude value Kε. The predetermined angular velocity aβ is set in advance according to the operating conditions of the engine 1, such as the engine speed and required torque, and is stored in the memory unit 52 of the ECU 50 as, for example, a characteristics map.

[0049] After switching to SI combustion, the ECU 50 crank angular acceleration d 2 θ / d 2 When t is less than a predetermined angular velocity aβ and the amplitude value K is less than a predetermined amplitude value Kε, it is determined that SI combustion is being performed stably. 2 θ / d 2 When t becomes equal to or greater than a predetermined angular velocity aβ or when the amplitude value K becomes equal to or greater than a predetermined amplitude value Kε, the spark plug 14 is controlled to retard the ignition timing. 2 θ / d 2 By retarding the ignition timing until t becomes less than a predetermined angular velocity aβ and the amplitude value K becomes less than a predetermined amplitude value Kε, it is possible to stabilize SI combustion.

[0050] 7 to 13 are flowcharts showing an example of a combustion mode switching process executed by the ECU 50 of FIG. 4. The processes of FIGS. 7 to 13 are repeatedly executed at a predetermined cycle while the engine 1 is operating. As shown in FIG. 7, first, in step S1, a characteristic map stored in the memory unit 52 is referenced to identify the optimal combustion mode according to the operating conditions of the engine 1. Next, in step S2, it is determined whether or not the currently executed combustion mode differs from the optimal combustion mode identified in step S1 and it is necessary to switch the combustion mode. If the result in step S2 is affirmative, the process proceeds to step S3, and the switching process of FIGS. 8 to 13 is executed. If the result in step S2 is negative, the process ends.

[0051] FIG. 8 shows an example of a switching process when switching from SI combustion to HCCI combustion. As shown in FIG. 8, first, in step S10, it is determined whether the amplitude value K is less than a predetermined amplitude value Kα and the peroxide concentration C2 is equal to or greater than a predetermined concentration Cα. If the result in step S10 is affirmative, the process proceeds to step S11, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform HCCI combustion using reformed fuel. Then, in step S12, it is determined whether the amplitude value K is less than a predetermined amplitude value Kα. If the result in step S12 is affirmative, it is determined that the combustion is stably performed, and the process is terminated. If the result in step S12 is negative, the process proceeds to step S13, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform HCCI combustion using gasoline fuel. Then, in step S14, it is determined whether the amplitude value K is less than a predetermined amplitude value Kα. If the result in step S14 is affirmative, it is determined that the combustion is stably performed, and the process is terminated. If the result in step S14 is NO, the process proceeds to step S15, where the electric pumps 31, 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform SI combustion using gasoline fuel.

[0052] FIG. 9 shows an example of a switching process when switching from HCCI combustion to SI combustion. As shown in FIG. 9, first, in step S20, it is determined whether or not the amplitude value K is equal to or greater than a predetermined amplitude value Kα. If the result in step S20 is affirmative, the process proceeds to step S21, where the electric pumps 31, 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform SI combustion using gasoline fuel. Next, in step S22, it is determined whether or not the amplitude value K is less than a predetermined amplitude value Kα. If the result in step S22 is affirmative, it is determined that the combustion is stable, and the process ends. If the result in step S22 is negative, the process proceeds to step S23, where the spark plug 14 is controlled to retard the ignition timing. If the result in step S20 is negative, the process proceeds to step S24, where the electric pumps 31, 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to continue HCCI combustion.

[0053] FIG. 10 shows an example of a switching process when switching from HCCI combustion to SAHCCI combustion. As shown in FIG. 10, first, in step S30, the crank angular acceleration d 2 θ / d 2 It is determined whether t is equal to or greater than a predetermined angular velocity aα, the amplitude value K is less than a predetermined amplitude value Kβ, and the peroxide concentration C2 is equal to or greater than a predetermined concentration Cβ. If the result in step S30 is YES, the process proceeds to step S31, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform SAHCCI combustion using reformed fuel. Next, in step S32, the crank angular acceleration d 2 θ / d 2 It is determined whether t is less than a predetermined angular velocity aα and whether the amplitude value K is less than a predetermined amplitude value Kβ. If the result in step S32 is YES, it is determined that the combustion is stable, and the process ends. If the result in step S32 is NO, the process proceeds to step S33, where the ignition plug 14 is controlled to retard the ignition timing.

[0054] If the result in step S30 is negative, the process proceeds to step S34, where it is determined whether the peroxide concentration C2 is less than the predetermined concentration Cβ. If the result in step S34 is positive, the process proceeds to step S35, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform SI combustion using gasoline fuel. Next, in step S36, the crank angular acceleration d 2 θ / d 2 It is determined whether t is less than a predetermined angular velocity aα and whether the amplitude value K is less than a predetermined amplitude value Kβ. If the result in step S36 is YES, it is determined that combustion is stable and the process ends. If the result in step S36 is NO, the process proceeds to step S37, where the spark plug 14 is controlled to retard the ignition timing. If the result in step S34 is NO, the process proceeds to step S38, where the electric pumps 31, 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled to continue HCCI combustion.

[0055] FIG. 11 shows an example of a switching process when switching from SAHCCI combustion to HCCI combustion. As shown in FIG. 11, first, in step S40, the crank angular acceleration d 2 θ / d 2 It is determined whether t is less than a predetermined angular velocity aα, the amplitude value K is equal to or greater than a predetermined amplitude value Kβ, and the peroxide concentration C2 is equal to or greater than a predetermined concentration Cγ. If the result in step S40 is positive, the process proceeds to step S41, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform HCCI combustion using reformed fuel. Then, in step S42, it is determined whether the amplitude value K is less than a predetermined amplitude value Kβ. If the result in step S42 is positive, it is determined that the combustion is stable, and the process ends. If the result in step S42 is negative, the process proceeds to step S43, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform HCCI combustion using gasoline fuel. If the result in step S40 is negative, the process proceeds to step S44, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to continue SAHCCI combustion.

[0056] FIG. 12 shows an example of a switching process when switching from SI combustion to diffusion combustion. As shown in FIG. 12, first, in step S50, it is determined whether or not the amplitude value K is equal to or greater than a predetermined amplitude value Kγ. If the result in step S50 is affirmative, the process proceeds to step S51, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform diffusion combustion using reformed fuel. Next, in step S52, it is determined whether or not the amplitude value K is less than a predetermined amplitude value Kε. If the result in step S52 is affirmative, it is determined that combustion is stable, and the process ends. If the result in step S52 is negative, the process proceeds to step S53, where the injector 13 is controlled to retard the injection timing. If the result in step S50 is negative, the process proceeds to step S54, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to continue SI combustion using gasoline fuel.

[0057] FIG. 13 shows an example of a switching process when switching from diffusion combustion to SI combustion. As shown in FIG. 13, first, in step S60, the crank angular acceleration d 2 θ / d 2 It is determined whether t is equal to or greater than a predetermined angular velocity aβ and the amplitude value K is less than a predetermined amplitude value Kε. If the result in step S60 is YES, the process proceeds to step S61, where the electric pumps 31 and 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled so as to perform SI combustion using gasoline fuel. Next, in step S62, the crank angular acceleration d 2 θ / d 2 It is determined whether t is less than a predetermined angular velocity aβ and whether the amplitude value K is less than a predetermined amplitude value Kε. If the result in step S62 is YES, it is determined that combustion is stable and the process ends. If the result in step S62 is NO, the process proceeds to step S63, where the spark plug 14 is controlled to retard the ignition timing. If the result in step S60 is NO, the process proceeds to step S64, where the electric pumps 31, 33, the throttle valve 12, the injector 13, and the spark plug 14 are controlled to continue diffusion combustion using reformed fuel.

[0058] According to this embodiment, the following advantageous effects can be obtained. (1) The device 100 includes an engine 1 having an injector 13 that injects fuel into the combustion chamber 10 and an ignition plug 14 that ignites a mixture of fuel and air in the combustion chamber 10, and an ECU 50 that controls the injector 13 and the ignition plug 14 so as to switch the combustion mode according to the required torque of the engine 1 (FIGS. 2, 4, and 7). The combustion modes include SI combustion involving ignition of gasoline fuel, HCCI combustion without ignition of reformed fuel in which part of the gasoline fuel is reformed into peroxide, SAHCCI combustion involving ignition of reformed fuel, and diffusion combustion without ignition of reformed fuel (FIG. 6).

[0059] The ECU 50 controls the injector 13 and the spark plug 14 so as to switch the combustion mode to SAHCCI combustion when the required torque is less than the first predetermined value Te1, to switch the combustion mode to HCCI combustion when the required torque is equal to or greater than the first predetermined value Te1 and less than a second predetermined value Te2 that is greater than the first predetermined value Te1, to switch the combustion mode to SI combustion when the required torque is equal to or greater than the second predetermined value Te2 and less than a third predetermined value Te3 that is greater than the second predetermined value Te2, and to switch the combustion mode to diffusion combustion when the required torque is equal to or greater than the third predetermined value Te3 (FIGS. 6 to 13). In this way, the combustion mode is switched according to the required torque of the engine 1, and the optimal combustion mode is adopted, thereby improving the thermal efficiency over the entire operating range of the engine 1.

[0060] (2) The device 100 includes a concentration sensor 24a that detects a peroxide concentration C2 of the fuel injected into the combustion chamber 10, and a knock sensor 18 that detects an amplitude value K of the vibration of the engine 1 (FIG. 4). The ECU 50 controls the injector 13 and the spark plug 14 to switch from SI combustion to HCCI combustion under the condition that the amplitude value K detected by the knock sensor 18 is less than a predetermined amplitude value Kα and the peroxide concentration C2 detected by the concentration sensor 24a is equal to or greater than a predetermined concentration Cα (FIG. 8).

[0061] (3) The device 100 includes a knock sensor 18 that detects an amplitude value K of vibration of the engine 1 (FIG. 4). The ECU 50 controls the injector 13 and the spark plug 14 to switch from HCCI combustion to SI combustion on the condition that the amplitude value K detected by the knock sensor 18 is equal to or greater than a predetermined amplitude value Kα (FIG. 9).

[0062] By adopting SI combustion in the medium load range of the engine 1 and HCCI combustion in the low load range, it is possible to eliminate the decrease in thermal efficiency due to pumping loss and improve the thermal efficiency in the low load range of the engine 1. At this time, by switching the combustion type on the condition that the vibration amplitude value K of the engine 1 and the peroxide concentration C2 satisfy predetermined conditions, it is possible to ensure the stability of combustion when switching the combustion type.

[0063] (4) The device 100 includes a crank angle sensor 17 that detects the crank angle θ of the engine 1, a concentration sensor 24a that detects the peroxide concentration C2 of the fuel injected into the combustion chamber 10, and a knock sensor 18 that detects the amplitude value K of the vibration of the engine 1 (FIG. 4). The ECU 50 calculates the crank angular acceleration d 2 θ / d 2 t is calculated, and the calculated crank angular acceleration d 2 θ / d 2 The injector 13 and the spark plug 14 are controlled to switch from HCCI combustion to SAHCCI combustion under the conditions that t is equal to or greater than a predetermined angular velocity aα, the amplitude value K detected by the knock sensor 18 is less than a predetermined amplitude value Kβ, and the peroxide concentration C2 detected by the concentration sensor 24a is equal to or greater than a predetermined concentration Cβ (FIG. 10).

[0064] (5) The device 100 includes a crank angle sensor 17 that detects a crank angle θ of the engine 1, a concentration sensor 24a that detects a peroxide concentration C2 of the fuel injected into the combustion chamber 10, and a knock sensor 18 that detects an amplitude value K of vibration of the engine 1 (FIG. 4). The ECU 50 calculates a crank angular acceleration d 2 θ / d2 t is calculated, and the calculated crank angular acceleration d 2 θ / d 2 The injector 13 and the spark plug 14 are controlled to switch from SAHCCI combustion to HCCI combustion under the conditions that t is less than a predetermined angular velocity aα, the amplitude value K detected by the knock sensor 18 is equal to or greater than a predetermined amplitude value Kβ, and the peroxide concentration C2 detected by the concentration sensor 24a is equal to or greater than a predetermined concentration Cγ (FIG. 11).

[0065] Among the low load ranges of the engine 1, the extremely low load range where the required torque is particularly small is where SAHCCI combustion is adopted, and the stability of combustion in the extremely low load range can be ensured by assisting the self-ignition of fuel through ignition. At this time, the vibration amplitude value K of the engine 1, the peroxide concentration C2, and the crank angular acceleration d 2 θ / d 2 By switching the combustion type on the condition that t satisfies a predetermined condition, it is possible to ensure the stability of combustion when switching the combustion type.

[0066] (6) The device 100 includes a knock sensor 18 that detects an amplitude value K of vibration of the engine 1 (FIG. 4). The ECU 50 controls the injector 13 and the spark plug 14 to switch from SI combustion to diffusion combustion when the amplitude value K detected by the knock sensor 18 is equal to or greater than a predetermined amplitude value Kγ (FIG. 12).

[0067] (7) The device 100 includes a crank angle sensor 17 that detects a crank angle θ of the engine 1, and a knock sensor 18 that detects an amplitude value K of vibration of the engine 1 (FIG. 4). The ECU 50 calculates a crank angular acceleration d 2 θ / d 2 t is calculated, and the calculated crank angular acceleration d 2 θ / d 2 On the condition that t is equal to or greater than a predetermined angular velocity aβ and the amplitude value K detected by the knock sensor 18 is less than a predetermined amplitude value Kε, the injector 13 and the spark plug 14 are controlled to switch from diffusion combustion to SI combustion (FIG. 13).

[0068] By adopting SI combustion in the medium load range of the engine 1 and diffusion combustion in the high load range, it is possible to eliminate the decrease in thermal efficiency caused by retarding the ignition timing to avoid knocking, and improve the thermal efficiency in the high load range of the engine 1. At this time, the vibration amplitude value K of the engine 1 and the crank angular acceleration d 2 θ / d 2 By switching the combustion type on the condition that t satisfies a predetermined condition, it is possible to ensure the stability of combustion when switching the combustion type.

[0069] In the above embodiment, the internal configuration of the engine 1 has been described by way of example in FIG. 2 and the like, but the internal configuration of the engine, such as the arrangement of the injectors and spark plugs, is not limited to that shown in the figure.

[0070] In the above embodiment, an example is described in which the reformed fuel reformed on-board by the reformer 22 mounted on the vehicle is used, but the reformed fuel in which part of the gasoline fuel is reformed into peroxide is not limited to this. For example, the reformed fuel may be a fuel that is produced in advance and stored in the vehicle fuel tank.

[0071] 3, 4, etc., an example has been described in which the reformed fuel is stored in the reformed fuel tank 23 and the ECU 50 controls the electric pump 33 and the injector 13 to supply the reformed fuel to the engine 1, but the control unit that controls the injector is not limited to this. For example, the electric pump 26 and the heater 27 may be controlled instead of the electric pump 33 to switch the reformer 22 on and off, or to adjust the reforming rate and amount of reforming by the reformer 22, thereby supplying the reformed fuel to the engine 1. In this case, the reformed fuel tank 23 and the electric pump 33 may not be provided.

[0072] In the above embodiment, an example in which the mixer 24 for mixing the gasoline fuel and the reformed fuel is provided has been described with reference to FIG. 3 etc., but if a sufficient amount of reformed fuel can be supplied, the mixer 24 does not need to be provided.

[0073] The above description is merely an example, and the present invention is not limited to the above-mentioned embodiment and modifications, as long as the features of the present invention are not impaired. The above-mentioned embodiment and one or more modifications can be arbitrarily combined, and modifications can be combined with each other. [Explanation of symbols]

[0074] 1 engine, 10 combustion chamber, 13 injector, 14 spark plug, 17 crank angle sensor, 18 knock sensor, 20 fuel supply passage, 21 fuel tank, 22 reformer, 23 reformed fuel tank, 23a, 24a concentration sensor, 24 mixer, 26, 31, 33 electric pump, 27 heater, 50 ECU, 51 processing unit, 52 memory unit, 100 engine control device (device)

Claims

1. An engine having an injector that injects fuel into a combustion chamber and an ignition plug that ignites a mixture of fuel and air in the combustion chamber; a control unit that controls the injector and the spark plug so as to switch the combustion mode in accordance with a required torque of the engine, the combustion forms include spark ignition combustion accompanied by ignition of gasoline fuel, first homogeneous charge compression ignition combustion accompanied by ignition of reformed fuel obtained by reforming a part of the gasoline fuel into peroxide, second homogeneous charge compression ignition combustion accompanied by ignition of the reformed fuel, and diffusion combustion accompanied by ignition of the reformed fuel, an ignition combustion mode switching unit that switches the combustion type to the first homogeneous charge compression ignition combustion mode when the required torque is equal to or greater than the first predetermined value and is less than a second predetermined value that is greater than the first predetermined value; an ignition combustion mode switching unit that switches the combustion type to the spark ignition combustion mode when the required torque is equal to or greater than the second predetermined value and is less than a third predetermined value that is greater than the second predetermined value; and an ignition combustion mode switching unit that switches the combustion type to the diffusion combustion mode when the required torque is equal to or greater than the third predetermined value.

2. 2. The engine control device according to claim 1, a concentration sensor for detecting a peroxide concentration in the fuel injected into the combustion chamber; A knock sensor for detecting an amplitude value of vibration of the engine is further provided. The control unit controls the injector and the spark plug to switch from the spark ignition combustion to the first homogeneous charge compression ignition combustion under the condition that the amplitude value detected by the knock sensor is less than a predetermined amplitude value and the peroxide concentration detected by the concentration sensor is equal to or greater than a predetermined concentration.

3. 2. The engine control device according to claim 1, A knock sensor is further provided for detecting an amplitude value of vibration of the engine. The engine control device is characterized in that the control unit controls the injector and the spark plug to switch from the first homogeneous charge compression ignition combustion to the spark ignition combustion on the condition that the amplitude value detected by the knock sensor is equal to or greater than a predetermined amplitude value.

4. 2. The engine control device according to claim 1, a crank angle sensor for detecting a crank angle of the engine; a concentration sensor for detecting a peroxide concentration in the fuel injected into the combustion chamber; A knock sensor for detecting an amplitude value of vibration of the engine is further provided. the control unit calculates a crank angular acceleration based on the crank angle detected by the crank angle sensor, and controls the injector and the spark plug to switch from the first homogeneous charge compression ignition combustion to the second homogeneous charge compression ignition combustion under the conditions that the calculated crank angular acceleration is equal to or greater than a predetermined angular velocity, the amplitude value detected by the knock sensor is less than a predetermined amplitude value, and the peroxide concentration detected by the concentration sensor is equal to or greater than a predetermined concentration.

5. 2. The engine control device according to claim 1, a crank angle sensor for detecting a crank angle of the engine; a concentration sensor for detecting a peroxide concentration in the fuel injected into the combustion chamber; A knock sensor for detecting an amplitude value of vibration of the engine is further provided. the control unit calculates a crank angular acceleration based on the crank angle detected by the crank angle sensor, and controls the injector and the spark plug to switch from the second homogeneous charge compression ignition combustion to the first homogeneous charge compression ignition combustion under the conditions that the calculated crank angular acceleration is less than a predetermined angular velocity, the amplitude value detected by the knock sensor is equal to or greater than a predetermined amplitude value, and the peroxide concentration detected by the concentration sensor is equal to or greater than a predetermined concentration.

6. 2. The engine control device according to claim 1, A knock sensor is further provided for detecting an amplitude value of vibration of the engine. The control unit controls the injector and the spark plug to switch from the spark ignition combustion to the diffusion combustion on condition that the amplitude value detected by the knock sensor is equal to or greater than a predetermined amplitude value.

7. 2. The engine control device according to claim 1, a crank angle sensor for detecting a crank angle of the engine; A knock sensor for detecting an amplitude value of vibration of the engine is further provided. the control unit calculates a crank angular acceleration based on the crank angle detected by the crank angle sensor, and controls the injector and the spark plug to switch from the diffusion combustion to the spark ignition combustion under the condition that the calculated crank angular acceleration is equal to or greater than a predetermined angular velocity and the amplitude value detected by the knock sensor is less than a predetermined amplitude value.

Images