JP2017180197A - Control device of multi-cylinder engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an engine capable of efficiently heating a catalyst while improving fuel consumption in starting the engine.SOLUTION: A control device of a multi-cylinder engine in which SI combustion and CI combustion are switched, includes a plurality of exhaust valves respectively disposed in cylinders, an exhaust-side variable valve mechanism controlling lift timings of the exhaust valves independently from each other, and a catalyst disposed at an exhaust side with respect to the exhaust valves. In a case when a temperature of the multi-cylinder engine is a prescribed temperature or less, the SI combustion is executed while controlling an air-fuel ratio so that a ratio of air and fuel in the cylinder becomes a theoretical air-fuel ratio in the specific cylinder, and in the remaining cylinders, the CI combustion is executed by opening the exhaust valves at a prescribed timing of an intake stroke by using the exhaust-side variable valve mechanism, so that a burned gas discharged from the specific cylinder is taken into the cylinders and the air-fuel ratio is controlled to the air-fuel ratio higher than that of the specific cylinder.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a control device for a multi-cylinder engine.

  2. Description of the Related Art Conventionally, it is known to switch a fuel combustion method in an engine combustion chamber according to an engine operating state such as an engine speed, an engine load, and an engine temperature (water temperature). As a combustion system, an SI (Spark Ignition) combustion system in which fuel injected into the combustion chamber of the engine is ignited by spark ignition in a state where the engine speed and engine load are low, and an engine in which the engine speed and engine load are high. A CI (Compression Ignition) combustion method is known in which fuel injected into a combustion chamber is self-ignited by compression of the combustion chamber.

  In such an engine, in a state where the engine water temperature is low, such as immediately after the engine is started, cranking for driving the engine by the cell motor is first performed. Then, after reaching the complete explosion state where the engine can be driven by the combustion of the fuel, the engine warm-up operation is started by SI combustion in which the ignition timing is retarded in all the cylinders. In general, the use of CI combustion improves fuel efficiency compared to SI combustion, but compression self-ignition of fuel in the combustion chamber cannot be performed when the engine water temperature is low. Therefore, the engine is warmed up by SI combustion until the water temperature of the engine reaches a predetermined temperature or higher. Then, after the engine water temperature becomes equal to or higher than the predetermined temperature, the combustion system is switched from SI combustion to CI combustion for all cylinders. Patent Document 1 is known as a technique for switching the combustion method.

JP 2004-239217 A

  In Patent Document 1, fuel consumption and exhaust emission are improved by switching from SI combustion to CI combustion one cylinder at a time after engine startup in a state where the engine water temperature is low.

  In general, when SI combustion is compared with CI combustion, it is desirable to increase the time of CI combustion in an engine that switches between SI combustion and CI combustion because CI combustion has higher thermal efficiency and better fuel efficiency.

  On the other hand, in the CI combustion method, although the thermal efficiency is high, the temperature of the exhaust gas during combustion tends to be lower than the exhaust gas during SI combustion, so that the temperature in the cylinder hardly rises and the water temperature of the engine hardly rises. Therefore, if the CI combustion is frequently used at the time of starting the engine, the time required for warming up becomes longer, so that the fuel efficiency may not be substantially improved.

  Further, a catalyst for purifying exhaust gas is provided in the exhaust system of the engine, but in order for these catalysts to act effectively, it is necessary to warm up the catalyst by exhaust of the engine. However, as described above, the temperature of the exhaust gas during the CI combustion is relatively low. Therefore, if the CI combustion is frequently used when starting the engine, the catalyst may not be sufficiently warmed.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an engine control device that can efficiently warm a catalyst while improving fuel efficiency when starting an engine. To do.

  In order to solve the above-described problems, the present invention is a control apparatus for a multi-cylinder engine that switches a fuel combustion method between SI combustion and CI combustion according to the operating state of the engine, and includes a plurality of cylinders provided for each cylinder. An exhaust valve, an exhaust-side variable valve mechanism that controls the lift timing of the plurality of exhaust valves independently of each other, and a catalyst provided on the exhaust side of the exhaust valve, the temperature of the multi-cylinder engine When the temperature is equal to or lower than a predetermined temperature, for a specific cylinder among the plurality of cylinders, SI combustion is performed while controlling the air-fuel ratio so that the ratio of air and fuel in the cylinder becomes the stoichiometric air-fuel ratio. For the remaining cylinders, the exhaust valve is opened at a predetermined timing of the intake stroke using the exhaust side variable valve mechanism, and the burned gas discharged from the specific cylinder is taken into the cylinder. , Serial performing CI combustion while controlling the air-fuel ratio so that a high air-fuel ratio than the specific cylinder.

  According to the present invention thus configured, SI combustion is performed for a specific cylinder with the air-fuel ratio as the stoichiometric air-fuel ratio. As a result, it is possible to increase the engine temperature by exhausting high-temperature exhaust while improving fuel efficiency. Further, by discharging high-temperature exhaust gas by SI combustion for a specific cylinder, it is possible to warm the catalyst by providing high-temperature exhaust gas to the catalyst provided in the engine exhaust system. Further, with respect to the remaining cylinders, CI combustion is performed with the air-fuel ratio being higher than the stoichiometric air-fuel ratio, and the exhaust valve is opened during the intake stroke, whereby high-temperature exhaust exhausted from a specific cylinder is taken into the combustion chamber. The temperature in the remaining cylinders can be raised.

  Preferably, in the present invention, the combustion system of the cylinder performing SI combustion is switched to CI combustion and the combustion system of the cylinder performing CI combustion is switched to SI combustion every predetermined cycle.

  According to the present invention configured as described above, the temperature in the cylinder can be uniformly increased for all the cylinders by switching the combustion method at every predetermined cycle.

  In the present invention, preferably, the number of cylinders that perform CI combustion is increased stepwise, and the number of cylinders that perform SI combustion is decreased stepwise.

  According to the present invention configured as described above, the number of cylinders that perform CI combustion with high thermal efficiency is increased stepwise, and the number of cylinders that perform SI combustion is decreased stepwise, thereby improving the fuel efficiency of the entire engine. Can be made.

  Preferably, in the present invention, the stepwise increase in the number of cylinders that perform CI combustion and the stepwise decrease in the number of cylinders that perform SI combustion are performed according to the engine water temperature.

  According to the present invention configured as described above, the number of cylinders that perform CI combustion can be increased according to the water temperature of the engine, so that the number of cylinders that perform CI combustion more efficiently can be increased.

  In the present invention, it is preferable that the multi-cylinder engine is an in-line multi-cylinder engine, and the cylinder that performs CI combustion in the initial stage is a cylinder in the center of a row of cylinders.

  According to the present invention configured as described above, the CI combustion can be performed from the cylinder in the center, in which the in-cylinder temperature easily rises, among the cylinders arranged in series. Thereby, the temperature of the engine can be raised more efficiently.

  In the present invention, preferably, the air-fuel ratio λ of the remaining cylinders is about 2.

  According to the present invention configured as above, the temperature in the cylinder can be increased by increasing the air-fuel ratio of the remaining cylinders.

  As described above, according to the present invention, it is possible to efficiently warm the catalyst while improving fuel efficiency when starting the engine.

1 is a schematic configuration diagram of an engine according to an embodiment of the present invention. It is a schematic block diagram of the cylinder block of the engine by embodiment of this invention. It is a control block diagram of the engine by the embodiment of the present invention. It is a flowchart which shows operation | movement of the engine by embodiment of this invention.

  Hereinafter, an engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  First, the configuration of an engine according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an engine according to an embodiment of the present invention.

  As shown in FIG. 1, the engine 1 is a gasoline engine mounted on a vehicle and supplied with fuel containing at least gasoline. The engine 1 is disposed under a cylinder block 11 in which a plurality of cylinders 18 are arranged in series, a cylinder head 12 disposed on the cylinder block 11, and the cylinder block 11, and stores engine oil. And an oil pan 13. A piston 14 connected to the crankshaft 15 via a connecting rod 142 is fitted in each cylinder 18 so as to be able to reciprocate. The top surface of the piston 14 is provided with a cavity 141 that forms a reentrant combustion chamber that is applied to the combustion chamber of a diesel engine. The cavity 141 is opposed to the injector 67 when the piston 14 is positioned near the compression top dead center. The cylinder head 12, the cylinder 18, and the piston 14 having the cavity 141 define a combustion chamber 19. The shape of the combustion chamber 19 is not limited to the shape illustrated. For example, the shape of the cavity 141, the top surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber 19, and the like can be changed as appropriate.

  FIG. 2 is a schematic configuration diagram of a cylinder block of the engine. In this example, as shown in FIG. 2, the engine 1 is an in-line four-cylinder engine in which four cylinders 18a, 18b, 18c, and 18d are arranged in series. The combustion chambers 19a, 19b, 19c, and 19d of each cylinder 18 are The intake port 16 is constituted by an intake side manifold and the exhaust port 17 is constituted by an exhaust side manifold. In the figure, the intake valve and the exhaust valve are omitted for convenience of explanation. The air from the intake port 16 branches off at the manifold portion and is distributed almost evenly to the combustion chambers 19a, 19b, 19c, 19d of each cylinder. The burned gas generated in the combustion chambers 19a, 19b, 19c, 19d is exhausted to the exhaust port 17 side as exhaust gas.

  The engine 1 is set to a relatively high geometric compression ratio of 15 or more for the purpose of improving the theoretical thermal efficiency, stabilizing compression ignition combustion, and the like. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 15-20.

  Referring to FIG. 1 again, the cylinder head 12 is provided with an intake valve 21 and an exhaust valve 22 that open and close the opening on the combustion chamber 19 side at the intake port 16 and the exhaust port 17, respectively.

  For each cylinder 18, an injector 67 that directly injects fuel into the cylinder 18 (direct injection) is attached to the cylinder head 12. The injector 67 is disposed so that its nozzle hole faces the inside of the combustion chamber 19 from the central portion of the ceiling surface of the combustion chamber 19. The injector 67 directly injects an amount of fuel into the combustion chamber 19 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1. In this example, the injector 67 is a multi-hole injector having a plurality of nozzle holes, although detailed illustration is omitted. Thereby, the injector 67 injects the fuel so that the fuel spray spreads radially from the center position of the combustion chamber 19. At the timing when the piston 14 is positioned near the compression top dead center, the fuel spray injected radially from the central portion of the combustion chamber 19 flows along the wall surface of the cavity 141 formed on the top surface of the piston. In other words, the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is positioned near the compression top dead center is contained therein. This combination of the multi-hole injector 67 and the cavity 141 is an advantageous configuration for shortening the mixture formation period and the combustion period after fuel injection. In addition, the injector 67 is not limited to a multi-hole injector, and may be an open valve type injector.

  A fuel tank (not shown) and the injector 67 are connected to each other by a fuel supply path. A fuel supply system 62 including a fuel pump 63 and a common rail 64 and capable of supplying fuel to the injector 67 at a relatively high fuel pressure is interposed on the fuel supply path. The fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 can store the pumped fuel at a relatively high fuel pressure. When the injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the injector 67. Here, although not shown, the fuel pump 63 is a plunger type pump and is driven by the engine 1. The fuel supply system 62 configured to include this engine-driven pump enables the fuel with a high fuel pressure of 30 MPa or more to be supplied to the injector 67. The fuel pressure may be set to about 120 MPa at the maximum. The pressure of the fuel supplied to the injector 67 is changed according to the operating state of the engine 1. The fuel supply system 62 is not limited to this configuration.

  An ignition plug 25 for forcibly igniting the air-fuel mixture in the combustion chamber 19 (specifically, spark ignition) is also attached to the cylinder head 12. In this example, the spark plug 25 is disposed through the cylinder head 12 so as to extend obliquely downward from the exhaust side of the engine 1. The tip of the spark plug 25 is disposed facing the cavity 141 of the piston 14 located at the compression top dead center.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 18. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 19 of each cylinder 18 is connected to the other side of the engine 1.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30, and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 is disposed downstream thereof. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 on the downstream side of the surge tank 33 is an independent passage branched for each cylinder 18, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 18.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 18 and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. A direct catalyst 41 and an underfoot catalyst 42 are connected downstream of the exhaust manifold in the exhaust passage 40 as exhaust purification devices for purifying harmful components in the exhaust gas. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and, for example, a three-way catalyst disposed in a flow path in the case.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the direct catalyst 41 in the exhaust passage 40 are used for returning a part of the exhaust gas to the intake passage 30. They are connected via a passage 50. The EGR passage 50 includes a main passage 51 in which an EGR cooler 52 for cooling the exhaust gas with engine coolant is disposed. The main passage 51 is provided with an EGR valve 511 for adjusting the recirculation amount of the exhaust gas to the intake passage 30.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as “PCM”) 10 as control means. The PCM 10 is constituted by a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units, and this PCM 10 constitutes a controller.

FIG. 2 is a control block diagram of the engine according to the embodiment of the present invention. As shown in FIG. 2, detection signals from various sensors SW1, SW2, SW4 to SW18 are input to the PCM 10. Specifically, on the downstream side of the air cleaner 31, the PCM 10 includes a detection signal of an air flow sensor SW 1 that detects a flow rate of fresh air, a detection signal of an intake air temperature sensor SW 2 that detects the temperature of fresh air, and an EGR passage 50. The detection signal of the EGR gas temperature sensor SW4 that is disposed in the vicinity of the connection portion with the intake passage 30 and detects the temperature of the external EGR gas, and the intake air that is attached to the intake port 16 and immediately before flowing into the cylinder 18 The detection signal of the intake port temperature sensor SW5 for detecting the temperature, the detection signal of the in-cylinder pressure sensor SW6 attached to the cylinder head 12 and detecting the pressure in the cylinder 18, and the vicinity of the connection portion of the EGR passage 50 in the exhaust passage 40 And the detection signals of the exhaust temperature sensor SW7 and the exhaust pressure sensor SW8 that detect the exhaust temperature and the exhaust pressure, respectively. And it is disposed on the upstream side of the direct catalyst 41, disposed between the detection signal of the linear O ₂ sensor SW9 for detecting the oxygen concentration in the exhaust gas, the direct catalyst 41 and underfoot catalyst 42 and the exhaust A detection signal of a lambda O ₂ sensor SW10 that detects the oxygen concentration of the engine, a detection signal of a water temperature sensor SW11 that detects the temperature of engine cooling water, a detection signal of a crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, A detection signal of an accelerator opening sensor SW13 that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle, detection signals of intake side and exhaust side cam angle sensors SW14 and SW15, and a fuel supply system A fuel pressure sensor S that is attached to the common rail 64 of 62 and detects the fuel pressure supplied to the injector 67. 16 a detection signal of a detection signal of the hydraulic sensor SW17 for detecting the oil pressure of the engine 1, and the detection signal of the oil temperature sensor SW18 for detecting the oil temperature of the engine oil, is input.

  The PCM 10 determines the state of the engine 1 and the vehicle by performing various calculations based on these detection signals, and controls the (direct injection) injector 67, the spark plug 25, and the intake valves 21a and 21b accordingly. Control for the intake side variable valve mechanism 71 that controls the exhaust valve 22a and 22b, the fuel supply system 62, and the actuators of various valves (throttle valve 36, EGR valve 511). Output a signal. Thus, the PCM 10 operates the engine 1.

  The intake-side variable valve mechanism 71 and the exhaust-side variable valve mechanism 72 are known so that the lift amount and lift timing of the corresponding intake valve 21 or exhaust valve 22 can be controlled independently from the other intake valves 21 or exhaust valves 22. Any variable valve mechanism may be used. For example, a hydraulic valve or an electromagnetic valve can be used.

  Next, the operation of the above-described engine control device will be described in detail.

  FIG. 4 is a flowchart showing the operation of the engine control apparatus. As shown in FIG. 4, for example, when the engine is started and a series of processes is started, in step S <b> 1, the PCM 10 determines whether or not the engine 1 has reached a complete explosion state. The complete explosion state refers to a state in which ignition of fuel is started after cranking operation and the engine can be driven by fuel combustion. The PCM 10 operates all the cylinders in the SI combustion method until the engine reaches a complete explosion state. When the engine reaches a complete explosion state and reaches a state where it can be driven without depending on the cell motor, the processes after step S2 are performed.

  In step S2, the PCM 10 sets the fuel combustion method for the specific three cylinders as the SI combustion method and the fuel combustion method as the CI combustion method for the remaining one cylinder. In this case, it is possible to appropriately select which of the four cylinders is used as the CI combustion method, but it is preferable to change the cylinder that performs the CI combustion every several cycles. Specifically, when the cylinder 18a shown in FIG. 2 is first operated by the CI combustion method and the remaining cylinders 18b, 18c, and 18d are operated by the SI combustion method, for example, after two cycles, the cylinder 18a is operated by the CI combustion method. The combustion method of the cylinder 18a is changed to the SI combustion method, and the combustion method of the cylinder 18b is changed to the CI combustion method instead. Thus, by changing the cylinders operated by the CI combustion method every several cycles, the temperatures in the combustion chambers 19 of all the cylinders 18 can be increased uniformly.

  Then, if the combustion method for the specific three cylinders in step S2 is the SI combustion method, the temperature of the exhaust gas from the cylinder operated by the SI combustion method is changed to the temperature of the exhaust gas from the cylinder operated by the CI combustion method. It can be higher than the temperature. Exhaust gas from the cylinders operated in the SI combustion system is supplied to the direct catalyst 41 and the underfoot catalyst 42 via the exhaust port 17. Thereby, the direct catalyst 41 and the underfoot catalyst 42 can be warmed up. In this case, the air-fuel ratio in the combustion chamber 19 of the cylinder operated by the SI combustion method is adjusted to the theoretical air-fuel ratio λ = 1. As a result, high-temperature exhaust can be discharged while improving fuel efficiency.

  The remaining one cylinder is operated by a CI combustion method with relatively high thermal efficiency and good fuel efficiency. For the cylinders operating in the CI combustion system, internal EGR processing is executed by opening the exhaust valve 22 at a predetermined amount and at a predetermined timing in the intake stroke, so-called exhaust double opening. In this case, the air-fuel ratio in the combustion chamber 19 of the cylinder 18 operated by the CI combustion method is higher than the air-fuel ratio in the combustion chamber 19 of the cylinder 18 operated by the SI combustion method, and is adjusted to, for example, around λ = 2. Is done. As a result, in the intake stroke, the high-temperature exhaust gas discharged from the adjacent cylinder operated in the SI combustion system to the exhaust port 17 can be taken into the combustion chamber 19 and the temperature in the combustion chamber 19 can be increased.

  Next, in step S3, the PCM 10 determines whether or not the water temperature of the engine 1 has become higher than a predetermined first threshold value T1. If the engine water temperature is not higher than the first threshold value T1, the combustion method determined in step S2 is maintained, and the operation of the engine is continued in this state.

  When the PCM 10 determines in step S3 that the water temperature of the engine 1 has become higher than the first threshold value T1, the PCM 10 performs the processing after step S4.

  In step S4, the PCM 10 switches the combustion method of the engine 1, sets the fuel combustion method for the specific two cylinders to the SI combustion method, and sets the fuel combustion method to the CI combustion method for the remaining two cylinders. Even in this case, it is possible to appropriately select which cylinder is used as the CI combustion method. However, in the example shown in FIG. 2, among the four cylinders arranged in series, the cylinders 18b and 18c at the center are selected. The combustion method is preferably a CI combustion method.

  Next, in step S5, the PCM 10 determines whether or not the water temperature of the engine 1 has become higher than a predetermined second threshold value T2 (T2> T1). If the engine water temperature is not higher than the second threshold value T2, the combustion method determined in step S4 is maintained, and the operation of the engine is continued in this state.

  If the PCM 10 determines in step S5 that the water temperature of the engine 1 has become higher than the second threshold value T2, the PCM 10 performs the processing from step S6.

  In step S6, the PCM 10 switches the combustion method of the engine 1, sets the fuel combustion method for the specific three cylinders to the SI combustion method, and sets the fuel combustion method to the CI combustion method for the remaining one cylinder.

  Next, in step S7, the PCM 10 determines whether or not the water temperature of the engine 1 has become higher than a predetermined third threshold value T3 (T3> T2). If the engine water temperature is not higher than the third threshold value T3, the combustion system determined in step S6 is maintained, and the engine operation is continued in this state.

  If the PCM 10 determines in step S7 that the water temperature of the engine 1 has become higher than the third threshold value T3, the PCM 10 performs the processes in and after step S8.

  In step S8, the PCM 10 assumes that the warm-up operation has been completed and sets the combustion method for all cylinders to the CI combustion method, and ends the series of processes.

  Table 1 below is a graph showing an example of the combustion system of each cylinder after the engine has reached the complete explosion state.

  Table 1 shows an example in which the number of cylinders operated by CI combustion is increased step by step while changing the cylinder that performs CI combustion every three cycles.

  As described above, the PCM 10 operates all the cylinders in the SI combustion method until the complete explosion state is reached, and thereafter, increases the number of cylinders that perform CI combustion in stages according to the engine water temperature, and performs SI combustion. Reduce the number of cylinders. Thus, the direct catalyst 41 and the underfoot catalyst 42 can be warmed up while gradually increasing the number of cylinders that perform CI combustion and improving fuel efficiency. In the present embodiment, the number of cylinders that perform CI combustion in stages is increased in accordance with the engine water temperature. However, time measurement is started after the engine reaches a complete explosion state, and a predetermined time has elapsed. You may make it increase the number of the cylinders operated by a CI combustion system whenever it does.

  In addition, as a cylinder operated by the CI combustion system, in the initial stage where the number of cylinders operated by the CI combustion system is small, the combustion system is used for the cylinder 18b or 18c in the center among the four cylinders arranged in series. The CI combustion method is preferable. This is because the two cylinders 18b and 18c are sandwiched between the cylinders 18a and 18d, so that the temperature of the combustion chambers 19b and 19c can be easily maintained during combustion.

1 engine 10 PCM
18 cylinder 22 exhaust valve 72 exhaust side variable valve mechanism

Claims (6)

A control device for a multi-cylinder engine that switches a fuel combustion method between SI combustion and CI combustion according to an engine operating state,
A plurality of exhaust valves provided for each cylinder;
An exhaust side variable valve mechanism for controlling the lift timing of the plurality of exhaust valves independently of each other;
A catalyst provided on the exhaust side of the exhaust valve,
When the temperature of the multi-cylinder engine is below a predetermined temperature,
For a specific cylinder of the plurality of cylinders, SI combustion is performed while controlling the air-fuel ratio so that the ratio of air to fuel in the cylinder becomes the stoichiometric air-fuel ratio, and for the remaining cylinders of the plurality of cylinders, The exhaust valve is opened at a predetermined timing of the intake stroke using the exhaust side variable valve mechanism, and the burned gas discharged from the specific cylinder is taken into the cylinder and is higher than the specific cylinder. A control apparatus for a multi-cylinder engine that performs CI combustion while controlling the air-fuel ratio so that the air-fuel ratio becomes the same.   2. The control of a multi-cylinder engine according to claim 1, wherein a combustion system of a cylinder performing SI combustion is switched to CI combustion and a combustion system of a cylinder performing CI combustion is switched to SI combustion every predetermined cycle. apparatus.   The control device for a multi-cylinder engine according to claim 1 or 2, wherein the number of cylinders that perform CI combustion is increased stepwise and the number of cylinders that perform SI combustion is decreased stepwise.   4. The control apparatus for a multi-cylinder engine according to claim 3, wherein the stepwise increase in the number of cylinders performing CI combustion and the stepwise decrease in the number of cylinders performing SI combustion are performed according to engine water temperature.   The multi-cylinder engine according to any one of claims 1 to 4, wherein the multi-cylinder engine is an in-line multi-cylinder engine, and a cylinder that performs CI combustion in an initial stage is a cylinder at a center of a row of cylinders. Control device.   The control device for a multi-cylinder engine according to any one of claims 1 to 5, wherein an air-fuel ratio λ of the remaining cylinders is about 2.

Images