JP2020133558A - Engine controller - Google Patents

Abstract

To suppress accidental fire under a low load situation in a gasoline engine adopting premixed compression ignition.SOLUTION: An engine controller estimates a combustion chamber wall surface temperature of a cylinder 12 in low-load HCCI control; when the estimated value of the combustion chamber wall surface temperature is less than a lower limit threshold value of a target wall surface temperature range, injects fuel into an auxiliary chamber 24 by an auxiliary chamber injector 26; and immediately after that, ignites an air-fuel mixture in the auxiliary chamber 24 by an ignition plug 27 to heat the wall surface of the cylinder 12 on a combustion chamber side, to increase the combustion chamber wall surface temperature.SELECTED DRAWING: Figure 1

Description

The present invention relates to an engine control device for a gasoline engine to which Homogeneous Charge Compression Ignition (HCCI) is applied.

Currently, research and development of gasoline engines to which premixed compression ignition is applied are underway. According to the premixed compression ignition, since the dilute premixed gas is self-ignited and combusted, the combustion temperature is lower than that of spark ignition (SI), and NOx can be significantly reduced. In addition, a high compression ratio can be realized and thermal efficiency can be improved.

In Patent Document 1 below, in a multi-cylinder 4-cycle gasoline engine, between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, the burnt gas lean-burned in the preceding cylinder in the exhaust stroke is in the intake stroke. The technique of introducing it into the succeeding cylinder and performing compression self-ignition in the succeeding cylinder is described.

Japanese Unexamined Patent Publication No. 2006-70859

However, in premixed compression ignition, the air-fuel mixture introduced into the cylinder is compressed by a piston to raise the temperature and self-ignite. Therefore, when the load on the engine is low, there is a problem that the temperature of the air-fuel mixture in the cylinder rises insufficiently and misfire is likely to occur.

The present invention has been made in view of, for example, the above-mentioned problems, and an object of the present invention is to provide an engine control device capable of suppressing a misfire under a low load condition in a gasoline engine to which premixed compression ignition is applied. To provide.

In order to solve the above problems, the present invention is an engine control device that controls a four-cycle engine, the intake passage injector that injects fuel into the air flowing through the intake passage connected to the combustion chamber in the cylinder of the engine. A sub chamber provided in the engine and communicating with the combustion chamber, a sub chamber injector for injecting fuel into the sub chamber, a spark plug for igniting an air-fuel mixture in the sub chamber, and an arithmetic processing device are provided. The arithmetic processing device performs spark ignition combustion control that burns fuel by igniting the air-fuel mixture in the sub-chamber with the spark plug according to the operating condition of the engine, and compresses the air-fuel mixture in the cylinder. When the combustion control switching unit that switches between the premixed compression ignition combustion control that burns the fuel by self-ignition and the premixed compression ignition combustion control is executed, and the estimated value of the temperature of the wall surface on the combustion chamber side of the cylinder. In one cycle consisting of the intake, compression, expansion, and exhaust strokes of the engine when the estimated value is less than a predetermined threshold when the wall temperature estimation unit is calculated and the premixed compression ignition combustion control is executed. It is provided with a wall surface heating control unit that heats the wall surface by controlling the sub-chamber injector and the spark plug so as to inject fuel at a predetermined injection timing and ignite at a predetermined ignition timing. It is characterized by being.

According to the present invention, it is possible to suppress misfire under a low load condition in a gasoline engine to which premixed compression ignition is applied.

It is explanatory drawing which shows the engine in the Example of this invention. It is a block diagram which shows the engine control device of the Example of this invention. It is explanatory drawing which shows the combustion control of the engine in the engine control device of the Example of this invention. In the embodiment of the present invention, an explanatory diagram showing the valve timings of the intake valve and the exhaust valve, the combustion injection timing of the intake passage injector, the combustion injection timing of the sub chamber injector, and the ignition timing of the spark plug in one cycle of the engine. is there. It is a flowchart which shows the combustion control in the engine control device of the Example of this invention. It is a flowchart which shows the wall surface temperature estimation process, the wall surface heat process, etc. in the engine control device of the Example of this invention.

The engine control device according to the embodiment of the present invention is an engine control device that controls a four-cycle engine, and is an intake passage injector that injects fuel into air flowing through an intake passage connected to a combustion chamber in the cylinder of the engine, and an engine. It is provided with a sub chamber that communicates with the combustion chamber, a sub chamber injector that injects fuel into the sub chamber, a spark plug that ignites the air-fuel mixture in the sub chamber, and an arithmetic processing device.

In addition, the arithmetic processing unit has a fuel control switching unit, a wall surface temperature estimation unit, and a wall surface heating control unit. The fuel control switching unit has spark ignition combustion control that burns fuel by igniting the air-fuel mixture in the sub-chamber with a spark plug, and premixed compression that burns fuel by compressing and self-igniting the air-fuel mixture in the cylinder. Ignition and combustion control is switched according to the operating conditions of the engine. The wall surface temperature estimation unit calculates an estimated value of the wall surface temperature on the combustion chamber side of the cylinder when the premixed compression ignition combustion control is executed. The wall surface heating control unit performs the engine intake, compression, expansion, and exhaust strokes when the estimated value of the wall surface on the combustion chamber side of the cylinder is less than a predetermined threshold during execution of premixed compression ignition combustion control. A wall surface that heats the wall surface on the combustion chamber side of the cylinder by controlling the sub-chamber injector and spark plug so that fuel injection is performed at a predetermined injection timing in one cycle consisting of the above and ignition is performed at a predetermined ignition timing. Perform heat treatment.

According to the engine control device of the present embodiment, when the estimated value of the temperature of the wall surface on the combustion chamber side of the cylinder is less than a predetermined threshold when the premixed compression ignition combustion control is executed, the sub chamber injector is used to perform the sub chamber. Fuel is injected into the engine, and the air-fuel mixture in the sub-chamber is ignited by the spark plug. As a result, the heat generated by the combustion of the air-fuel mixture in the sub-chamber can be used to heat the wall surface on the combustion chamber side of the cylinder, and the temperature of the wall surface can be raised. Since the temperature of the air-fuel mixture in the combustion chamber rises due to the rise in the temperature of the wall surface on the combustion chamber side of the cylinder, self-ignition of the fuel due to the compression of the air-fuel mixture in the cylinder is promoted, and misfire is less likely to occur. Therefore, misfire can be suppressed, and stable premixed compression ignition combustion can be realized.

(Engine control device)
FIG. 1 shows the engine 1 in the embodiment of the present invention. FIG. 2 shows an engine control device 5 according to an embodiment of the present invention. The engine 1 is a 4-cycle gasoline engine, which is mounted on a vehicle such as an automobile. A crankshaft is supported below the cylinder block 11 of the engine 1. Further, as shown in FIG. 1, a piston 13 is provided in the cylinder 12 arranged above the cylinder block 11, and the piston 13 is connected to the crankshaft via a connecting rod 14.

Further, the cylinder head 15 provided above the cylinder block 11 is provided with an intake valve 18 for opening and closing the intake port 16 and an exhaust valve 19 for opening and closing the exhaust port 17. Further, the valve operating mechanism provided in the cylinder head 15 is assembled with a variable valve mechanism 20 capable of changing the valve timings of the intake valve 18 and the exhaust valve 19. Further, an intake pipe 21 (intake manifold) is connected to the intake port 16, and an exhaust pipe 22 (exhaust manifold) is connected to the exhaust port 17.

Further, the engine 1 is provided with an intake passage injector 25. The intake passage injector 25 is attached in the vicinity of the intake port 16 or the vicinity of the intake pipe 21, and injects fuel into the intake air flowing through the intake port 16 or the intake pipe 21 toward the combustion chamber 23. The intake port 16 and the intake pipe 21 are specific examples of the "intake passage".

Further, a sub chamber 24 is formed in, for example, the cylinder head 15 of the engine 1. The sub chamber 24 communicates with the upper part of the combustion chamber 23 formed above the piston 13 in the cylinder 12. Further, an auxiliary chamber injector 26 and a spark plug 27 are provided in the vicinity of the auxiliary chamber 24.

The sub-chamber injector 26 is attached to, for example, a cylinder head 15 so that its fuel injection port is arranged in the sub-chamber 24 or in a position facing the sub-chamber 24. The sub chamber injector 26 injects fuel into the air-fuel mixture in the sub chamber 24 when a predetermined condition is satisfied during low load HCCI control described later.

The spark plug 27 is attached to, for example, the cylinder head 15 so that the ignition electrode is arranged in the sub chamber 24 or at a position facing the sub chamber 24. The spark plug 27 ignites by blowing sparks from the air-fuel mixture in the sub chamber 24 when a predetermined condition is satisfied during low-load HCCI combustion, which will be described later, or when SI is controlled.

Further, as shown in FIG. 2, the engine 1 includes a crank angle sensor 31 for detecting a crank angle, a rotation speed sensor 32 for detecting an engine rotation speed, an intake pressure sensor 33 for detecting an intake pressure, and cooling of the engine 1. A cooling water temperature sensor 34 or the like for detecting the water temperature (specifically, the temperature of the cooling water flowing through the cooling water passage (not shown) provided in the peripheral wall of the cylinder 12) is provided. Further, the vehicle equipped with the engine 1 is provided with an exhaust temperature sensor 35 for detecting the exhaust temperature, an accelerator opening sensor 36 for detecting the accelerator opening degree, and the like.

Further, the vehicle on which the engine 1 is mounted is provided with an ECU (engine control unit) 37 and a storage circuit 38. The ECU 37 includes, for example, a CPU (Central Processing Unit). The storage circuit 38 includes, for example, a semiconductor storage element. The crank angle sensor 31, the rotation speed sensor 32, the intake pressure sensor 33, the cooling water temperature sensor 34, the exhaust temperature sensor 35, and the accelerator opening sensor 36 are each connected to the ECU 37 and output a detection signal to the ECU 37. Further, the ECU 37 is connected to the variable valve mechanism 20, the intake passage injector 25, the auxiliary chamber injector 26, and the ignition circuit 39 that applies a voltage to the spark plug 27, and the ECU 37 controls these. Further, a storage circuit 38 is connected to the ECU 37, and the ECU 37 can read the information stored in the storage circuit 38 or write the information in the storage circuit 38. The ECU 37 is a specific example of the “arithmetic processing unit”, and the storage circuit 38 is a specific example of the “storage unit”.

The engine control device 5 of the embodiment of the present invention is composed of at least an intake passage injector 25, a sub chamber 24, a sub chamber injector 26, a spark plug 27, an ignition circuit 39, sensors 31 to 36, an ECU 37, and a storage circuit 38. ing.

The engine control device 5 controls the combustion of the engine 1. FIG. 3 shows the combustion control of the engine 1 in the engine control device 5. As shown in FIG. 3, the engine control device 5 selectively performs spark ignition combustion control and premixed compression ignition combustion control according to the operating condition of the engine 1. The spark ignition combustion control is a control for burning fuel by igniting the air-fuel mixture in the sub chamber 24 communicated with the combustion chamber 23 by the spark plug 27. The premixed compression ignition combustion control is a control for burning fuel by compressing the air-fuel mixture in the cylinder 12 and self-igniting it. Hereinafter, spark ignition combustion control is referred to as "SI control", and premixed compression ignition combustion control is referred to as "HCCI control". Specifically, the engine control unit 5, the engine speed is performed HCCI control when less than the predetermined revolution speed threshold N _a, performs SI control when the engine speed is more than the rotational speed threshold value N _a.

Further, the engine control device 5 selectively performs two types of HCCI control according to the operating condition of the engine. Specifically, when the magnitude of the load of the engine 1 is less than _a predetermined load threshold La, the engine control device 5 performs low load HCCI control (low load premixed compression ignition combustion control) to reduce the load of the engine 1. when the magnitude is above the load threshold L _a performing high load HCCI control (high load HCCI combustion control).

In the low load HCCI control, the engine control device 5 estimates the temperature of the wall surface of the cylinder 12 on the combustion chamber 23 side (hereinafter, this is referred to as “combustion chamber wall surface temperature”), and the estimated value of the combustion chamber wall surface temperature is calculated. The cylinder 12 by controlling the sub-chamber injector 26 and the ignition plug 27 to inject fuel at a predetermined injection timing in one cycle of the engine and ignite at a predetermined ignition timing when the temperature is less than a predetermined threshold. The wall surface on the combustion chamber 23 side of the above is heated. Hereinafter, the process of heating the wall surface of the cylinder 12 on the combustion chamber 23 side in this way is referred to as “wall surface heat treatment”. On the other hand, in the high load HCCI control, the engine control device 5 performs a process of estimating the combustion chamber wall surface temperature, a process of determining whether or not the estimated value of the combustion chamber wall surface temperature is less than a predetermined threshold value, and a wall surface heating process. Do not do either. Therefore, in the high load HCCI control, neither fuel injection by the sub chamber injector 26 nor ignition by the spark plug 27 is performed.

In order to perform such combustion control of the engine 1, the ECU 37 reads and executes a computer program stored in the storage circuit 38, thereby performing a combustion control switching unit 41, a wall surface temperature estimation unit 42, and a wall surface heating control unit 43. Functions as. The combustion control switching unit 41 switches between SI control and HCCI control based on the engine speed, and switches between low load HCCI control and high load HCCI control based on the magnitude of the load of the engine 1. The wall surface temperature estimation unit 42 estimates the temperature of the wall surface on the combustion chamber 23 side of the cylinder 12 in the low load HCCI control. The wall surface heating control unit 43 determines whether or not the estimated value of the combustion chamber wall surface temperature is less than a predetermined threshold value in the low load HCCI control, and when the estimated value of the combustion chamber wall surface temperature is less than the predetermined threshold value. Perform wall surface heat treatment.

FIG. 4 shows the valve timings of the intake valve 18 and the exhaust valve 19 in one cycle consisting of the intake, compression, expansion, and exhaust strokes of the engine 1, the combustion injection timing of the intake passage injector 25, and the combustion injection of the auxiliary chamber injector 26. The timing and the ignition timing of the spark plug 27 are shown.

In SI control by the engine control device 5, the valve timing of the intake valve 18 is set to the valve timing V _i1 shown by the broken line in FIG. 4, and the valve timing of the exhaust valve 19 is set to the valve timing V _e1 shown by the broken line in FIG. Is set to. Further, in each of the high load HCCI control and the low load HCCI control by the engine control device 5, the valve timing of the intake valve 18 is set to the valve timing _Vi2 shown by the solid line in FIG. 4, and the valve timing of the exhaust valve 19 is set. , The valve timing _Ve2 shown by the solid line in FIG. 4 is set.

In each of the high load HCCI control and the low load HCCI control, the valve timing of the exhaust valve 19 is advanced and the valve timing of the intake valve 18 is delayed as compared with the SI control. As a result, a negative overlap is formed, and combustion control using the high-temperature burned gas of the previous cycle, that is, combustion control applying internal EGR (internal exhaust gas recirculation) is performed. The valve timings of the intake valve 18 and the exhaust valve 19 are changed by the ECU 37 controlling the variable valve mechanism 20.

During addition, as shown in FIG. 4, SI control, in each of the high load HCCI control and low load HCCI control, injection timing _{P a} fuel intake passage injectors 25, the crank angle of 360 degrees about 90 degrees Is set to. Further, the concentration of fuel in the air-fuel mixture is different between SI control and HCCI control. That is, the concentration of fuel in the air-fuel mixture used for premixed compression ignition combustion in HCCI control is lower than the concentration of fuel in the air-fuel mixture used for spark ignition combustion in SI control. In each of the SI control and the HCCI control, the fuel injection amount of the intake passage injector 25 is controlled so that the fuel concentration in the air-fuel mixture becomes appropriate. Further, the ignition timing P _s of the spark plug 27 in the SI control is set between the crank angle of 720 degrees approximately 675 degrees. The fuel injection timing P _b of the sub-chamber injector 26 in the wall surface heat treatment executed by the low-load HCCI control will be described later. As described later, the ignition timing of the spark plug 27 on the wall surface heat treatment to be executed in a low load HCCI control is the same as the ignition timing P _s of the spark plug 27 in the SI control.

ただし、式（１）において、Ｔ_ｅｘは排気温度であり、θはクランク角であり、Ｖ_ｅｘは排気バルブ１９の開時における気筒１２内の体積であり、Ｖ（θ）は気筒１２内の体積であり、γは比熱比である。 (Estimation of combustion chamber wall surface temperature)
Here, an example of the method of estimating the wall surface temperature of the combustion chamber performed in the low load HCCI control will be described. The wall temperature of the combustion chamber is determined by the heat received from the combustion gas and the heat radiation to the cooling water. First, the combustion gas temperature T _g (θ) is calculated by the following equation (1).

However, in the equation (1), _Tex is the exhaust temperature, θ is the crank angle, _Vex is the volume in the cylinder 12 when the exhaust valve 19 is opened, and V (θ) is the volume in the cylinder 12. It is a volume, and γ is a specific heat ratio.

ただし、ｈは熱伝導率であり、Ａは燃焼室２３の表面積であり、Ｔ_ｗｇは燃焼室壁面温度である。 Further, the heat transfer amount dQ / dθ [W] from the combustion gas to the wall surface of the cylinder 12 on the combustion chamber side is generally expressed by the following equation (2).

However, h is the thermal conductivity, A is the surface area of the combustion chamber 23, and T _wg is the wall surface temperature of the combustion chamber.

ただし、Ｃ_ｈはモデル定数であり、Ｃ_ｍは平均ピストン速度であり、ｐは吸気圧であり、ｍａｘ（Ｔ_ｇ（θ））は最高燃焼ガス温度である。 Here, the thermal conductivity h is estimated by the following equation (3).

However, _Ch is a model constant, C _m is an average piston speed, p is an intake pressure, and max (T _g (θ)) is the maximum combustion gas temperature.

ただし、Ｄは燃焼室２３の壁面の厚さであり、ｋは熱伝導率である。 On the other hand, assuming one-dimensional steady heat conduction, there is a relationship shown in the following equation (4) between the combustion chamber wall surface temperature T _wg and the cooling water temperature T _w .

However, D is the thickness of the wall surface of the combustion chamber 23, and k is the thermal conductivity.

ただし、上線付きの変数はサイクル平均をとったものである。低負荷ＨＣＣＩ制御においては、上記式（１）〜（５）で推定した燃焼室壁面温度Ｔ_ｗｇが用いられる。以下、この燃焼室壁面温度Ｔ_ｗｇを、燃焼室壁面温度の推定値Ｔ_ｗｇと表現する。 From the above equations (1) to (4), the combustion chamber wall surface temperature T _wg can be estimated by the following equation (5).

However, the overlined variables are cycle averages. In the low load HCCI control, the combustion chamber wall surface temperature T _wg estimated by the above equations (1) to (5) is used. Hereinafter, the combustion chamber wall surface temperature T _wg, expressed as the estimated value T _wg of the combustion chamber wall temperature.

(Combustion control in engine control device)
FIG. 5 shows the flow of combustion control in the engine control device 5. This control is executed during the operation of the engine 1. The combustion control shown in FIG. 5, first, the combustion control switching unit 41 of the ECU37 is based on the detection signal from the speed sensor 32, the engine speed is equal to or less than the rotational speed threshold value N _a (step S1). When the engine speed is less than the rotational speed threshold value N _a (step S1: YES), then, the combustion control switching section 41, based on a detection signal from the accelerator opening sensor 36, the load of the engine 1 size it is equal to or less than the load threshold L _a (step S2). When the magnitude of the load of the engine 1 is less than the load threshold _{L a} (Step S2: YES), the engine control unit 5 executes a low-load HCCI control (step S3). On the other hand, in step S2, when the magnitude of the load of the engine 1 is not less than the load threshold _{L a} (Step S2: NO), the engine control unit 5 executes the high load HCCI control (step S3). On the other hand, in step S1, when the engine speed is not less than the rotational speed threshold value _{N a} (step S1: NO), the engine control unit 5 executes the SI control. The rotation speed threshold value N _a and load threshold L _a is previously stored in the memory circuit 38. The combustion control switching unit 41 performs the process of step S1 and step S2 in FIG. 5 reads the rotation speed threshold value N _a and load threshold L _a from the storage circuit 38.

FIG. 6 shows the flow of the wall surface temperature estimation process, the wall surface heat treatment, and the like. These processes are performed in the low load HCCI control of step S3 in FIG. In FIG. 6, first, the wall surface temperature estimation unit 42 of the ECU 37 receives the crank angle θ, the exhaust temperature _Tex , the intake pressure p, and the cooling from the crank angle sensor 31, the exhaust temperature sensor 35, the intake pressure sensor 33, and the cooling water temperature sensor 34. The water temperature T _w is acquired (step S11). Further, the wall surface temperature estimation unit 42 reads parameters necessary for estimating the combustion chamber wall surface temperature, such as the cylinder volume V (θ), the combustion chamber surface area A, and the combustion chamber wall surface thickness D, from the storage circuit 38. Further, the wall surface temperature estimation unit 42 calculates the in-cylinder volume V _ex when the exhaust valve 19 is opened, based on the crank angle θ, the in-cylinder volume V (θ), and the like.

Next, the wall surface temperature estimation unit 42 calculates the estimated value T _wg of the combustion chamber wall surface temperature using the information acquired or calculated in step S11 (step S12). The above-mentioned method for estimating the wall surface temperature of the combustion chamber can be used for calculating the estimated value T _wg of the wall temperature of the combustion chamber.

Next, the wall surface heating control unit 43 of the ECU 37 determines whether or not the estimated value T _wg of the combustion chamber wall surface temperature is less than the lower limit threshold value T _tc of the target wall surface temperature range (step S13). Here, the target wall surface temperature range is the range of the combustion chamber wall surface temperature that should be maintained when the HCCI control is executed. The target wall surface temperature range is acquired by, for example, a test, and is stored in advance in the storage circuit 38.

When the estimated value T _wg of the combustion chamber wall surface temperature is less than the lower limit threshold value T _tc of the target wall surface temperature range (step S13: YES), the wall surface heating control unit 43 performs the wall surface heating treatment. Steps S14 to S16 in FIG. 6 are wall surface heat treatments.

ただし、Ｃは気筒１２の壁面材質の比熱であり、Ｃ_Ｔは気筒１２の壁面厚さ係数であり、Ｈ_ｕは燃料の低位発熱量である。 In the wall surface heating treatment, first, the wall surface heating control unit 43 calculates the total injection amount M _f of the fuel injected into the sub chamber 24 by the sub chamber injector 26 in the low load HCCI control (step S14). In step S14, the wall surface heating control unit 43 increases the amount of heat required to raise the combustion chamber wall surface temperature from the estimated value T _wg of the combustion chamber wall surface temperature to the upper limit threshold T _th of the target wall surface temperature range, and lower heat generation of the fuel. The total injection amount M _f of the sub chamber injector 26 is calculated based on the amount. Specifically, the wall surface heating control unit 43 calculates the total injection amount M _f of the sub chamber injector 26 by the following equation (6).

However, C is the specific heat of the wall material of the cylinder 12, C _T is the wall thickness of the coefficient of the cylinder 12, H _u is the lower heating value of the fuel.

Next, the wall surface heating control unit 43 controls the sub chamber injector 26 and the spark plug 27, the combustion injection into the sub chamber 24 by the sub chamber injector 26, and the air-fuel mixture in the sub chamber 24 by the ignition plug 27. Ignition is performed (steps S15, S16). More specifically, as shown in FIG. 4, the fuel injection timing P _b of the sub chamber injector 26 is set while the crank angle is approximately 630 to 675 degrees in one cycle of the engine 1. .. Further, the ignition timing of the spark plug 27 on the wall surface heat treatment of the low load HCCI control, as well as the ignition timing P _s of the spark plug 27 in the SI control, is set between the crank angle of 720 degrees approximately 675 degrees There is. The wall surface heating control unit 43 controls the sub chamber injector 26 and the spark plug 27, and the total actual fuel injection amount by the sub chamber injector 26 in the wall surface heat treatment is the total injection amount of the sub chamber injector 26 calculated in step S14. Until M _f is reached, fuel injection at the injection timing P _b and ignition at the ignition timing P _s are repeated for each cycle of the engine 1. As a result, fuel into the sub chamber 24 in each cycle of the engine 1 until the total actual fuel injection amount by the sub chamber injector 26 reaches the total injection amount _Mf of the sub chamber injector 26 calculated in step S14. Injection and ignition of the air-fuel mixture in the auxiliary chamber 24 are performed.

By injecting fuel into the sub-chamber 24 and igniting the air-fuel mixture in the sub-chamber 24, the air-fuel mixture in the sub-chamber 24 is burned, and a high-temperature flame jet is emitted from the sub-chamber 24 into the combustion chamber 23. .. As a result, the wall surface of the cylinder 12 on the combustion chamber side is heated, and the combustion chamber wall surface temperature rises to the upper limit threshold _Tth of the target wall surface temperature range.

In the low load HCCI control, after the total fuel injection amount by the sub-chamber injector 26 in the wall surface heat treatment reaches the total injection amount _Mf of the sub-chamber injector 26 calculated in step S14, the sub-chamber injector The combustion injection by 26 and the ignition by the spark plug 27 are stopped, respectively.

On the other hand, in step 13, when the estimated value T _wg of the combustion chamber wall temperature is not less than the lower threshold T _tc the target wall surface temperature range (step S13: NO), the wall heating control unit 43 does not perform the wall heat treatment.

As described above, in the engine control device 5 of the embodiment of the present invention, the combustion chamber wall surface temperature of the cylinder 12 is estimated in the low load HCCI control, and the estimated value _Twg of the combustion chamber wall surface temperature is within the target wall surface temperature range. When it is less than the lower limit threshold T _tc , the fuel is injected into the sub chamber 24 by the sub chamber injector 26, and immediately after that, the combustion chamber wall surface temperature is adjusted by igniting the air-fuel mixture in the sub chamber 24 by the spark plug 27. Can be raised. Since the temperature of the air-fuel mixture in the combustion chamber 23 rises due to the rise in the wall surface temperature of the combustion chamber, self-ignition of the fuel due to the compression of the air-fuel mixture in the cylinder 12 is promoted, and misfire is less likely to occur. Therefore, misfire can be suppressed, and premixed compression ignition combustion can be stabilized.

Further, the engine control device 5 of this embodiment performs the wall surface heat treatment in the low load HCCI control and does not perform the wall surface heat treatment in the high load HCCI control. That is, in the HCCI control, is less than the load threshold L _a magnitude of the load of the engine 1, and the wall surface heat treatment when the estimated value T _wg of the combustion chamber wall temperature is below the lower threshold T _tc the target wall surface temperature range I do. When the engine 1 has a low load, the fuel concentration in the air-fuel mixture becomes lower than when the engine 1 has a high load. Therefore, misfire is likely to occur. By performing wall surface heating control only when a misfire is likely to occur in the operating state of the engine 1, the processing efficiency in combustion control can be improved.

Further, in the wall surface heat treatment, as can be seen from the above equation (6), the actual combustion chamber wall surface temperature is raised from the estimated value T _wg of the combustion chamber wall surface temperature to reach the upper limit threshold T _th of the target wall surface temperature range. The total fuel injection amount M _f by the sub-chamber injector 26 is calculated based on the amount of heat required for the fuel and the lower calorific value of the fuel. Then, until the total of the actual fuel injection amount by the sub-chamber injector 26 reaches the calculated total injection amount _Mf , the fuel injection by the sub-chamber injector 26 is repeated every cycle of the engine 1, and the sub-chamber injector 26 is used. After the total of the actual fuel injection amounts by the above reaches the total injection amount _Mf , the fuel injection by the sub chamber injector 26 is stopped. As a result, the HCCI control can be stabilized under a low load condition with the minimum required fuel injection amount.

In the above embodiment, the case of switching between the high load HCCI control and the low load HCCI control based on the load of the engine 1 has been given as an example. However, the present invention is not limited to this, and the control for switching between the high load HCCI control and the low load HCCI control may not be performed based on the load of the engine 1. That is, in the HCCI control, regardless of the magnitude of the load of the engine 1 performs the estimation of the combustion chamber wall temperature, when the estimated value T _wg of the combustion chamber wall temperature is below the lower threshold T _tc the target wall surface temperature range The wall surface heat treatment may be performed.

Further, in the above embodiment, the sub chamber 24 is formed in the cylinder head 15, but the sub chamber 24 may be provided in another place of the engine 1. For example, the auxiliary chamber 24 may be provided at a position close to the combustion chamber 23 in the cylinder block 11.

Further, in the above embodiment, the case where the spark plug 27 provided in the sub chamber 24 is used for ignition in SI control and ignition in wall surface heat treatment under low load HCCI control has been given as an example, but ignition for SI control has been given as an example. Two spark plugs, a plug and a spark plug for wall surface heat treatment, may be provided. In this case, the spark plug for SI control may be arranged so that the ignition electrode directly faces the combustion chamber 23.

Further, in the above embodiment, in the HCCI control, the valve timings of the intake valve 18 and the exhaust valve 19 are changed to form a negative overlap, so that the high-temperature burnt gas of the previous cycle is used to generate the fuel. A method of promoting self-ignition (a form of internal EGR) has been adopted, but the present invention is not limited to this. External EGR can also be adopted in HCCI control. When an external EGR is adopted, for example, an exhaust circulation pipe that returns the burned gas from the exhaust port 17 or the exhaust pipe 22 to the intake port 16 or the intake pipe 21, and a valve that controls the flow rate of the burned gas in the exhaust circulation pipe. Etc. are added to the engine 1.

Further, in the above embodiment, the case where the engine 1 mounted on a vehicle such as an automobile is controlled by the engine control device 5 has been given as an example, but the engine control device 5 of the present invention is, for example, an engine mounted on a ship or the like. It can also be applied to the control of 1.

Further, the present invention can be appropriately modified within the scope of the claims and within a range not contrary to the gist or idea of the invention that can be read from the entire specification, and the engine control device accompanied by such a modification is also the technical idea of the present invention. include.

1 engine 5 engine control device 12 cylinder 16 intake port (intake passage)
21 Intake pipe (intake passage)
23 Combustion chamber 24 Sub chamber 25 Intake passage injector 26 Sub chamber injector 27 Spark plug 37 ECU (calculation processing unit)
38 Storage circuit (storage unit)
41 Combustion control switching unit 42 Wall temperature estimation unit 43 Wall heating control unit

Claims (4)

An engine control device that controls a 4-cycle engine.
An intake passage injector that injects fuel into the air flowing through the intake passage connected to the combustion chamber in the cylinder of the engine.
A sub chamber provided in the engine and communicating with the combustion chamber,
A sub-chamber injector that injects fuel into the sub-chamber,
A spark plug that ignites the air-fuel mixture in the sub-chamber,
Equipped with an arithmetic processing unit
The arithmetic processing unit
Spark ignition combustion control that burns fuel by igniting the air-fuel mixture in the sub-chamber with the spark plug according to the operating condition of the engine, and fuel by compressing and self-igniting the air-fuel mixture in the cylinder. Combustion control switching unit that switches between premixed compression ignition combustion control and
When the premixed compression ignition combustion control is executed, the wall surface temperature estimation unit that calculates the estimated value of the wall surface on the combustion chamber side of the cylinder and the wall surface temperature estimation unit.
When the premixed compression ignition combustion control is executed, when the estimated value is less than a predetermined threshold value, fuel injection is performed at a predetermined injection timing in one cycle consisting of the intake, compression, expansion and exhaust strokes of the engine. An engine including a wall surface heating control unit that heats the wall surface by controlling the sub chamber injector and the spark plug so as to perform and ignite at a predetermined ignition timing. Control device. The wall surface heating control unit is described when the load magnitude of the engine is less than a predetermined magnitude and the estimated value is less than a predetermined threshold value at the time of executing the premixed compression ignition combustion control. The engine control device according to claim 1, wherein the wall surface heat treatment is performed. The arithmetic processing unit includes a storage unit.
The storage unit stores a target wall surface temperature range indicating the temperature range of the wall surface to be maintained when the premixed compression ignition combustion control is executed.
When the premixed compression ignition combustion control is executed, the wall surface heating control unit performs the wall surface heating treatment when the estimated value is less than the lower limit threshold value of the target wall surface temperature range.
In the wall surface heat treatment, the wall surface heating control unit uses the amount of heat required to raise the temperature of the wall surface from the estimated value until it reaches the upper limit threshold value of the target wall surface temperature range, and the amount of heat generated by the fuel. The engine control device according to claim 1 or 2, wherein the total injection amount of fuel by the chamber injector is calculated. The wall surface heating control unit injects fuel at the predetermined injection timing every cycle until the total actual fuel injection amount by the sub-chamber injector in the wall surface heat treatment reaches the calculated total injection amount. The engine control device according to claim 3, wherein the sub-chamber injector is controlled so as to be repeatedly performed.

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