JP7334403B2 - 2-stroke engine with supercharger - Google Patents

Description

The present invention belongs to the technical field related to a two-stroke engine with a supercharger.

2. Description of the Related Art Conventionally, a supercharged two-stroke engine having a supercharger provided in an intake passage is known (see, for example, Patent Document 1).

In Patent Document 1, in the scavenging period near the bottom dead center of the piston, both an intake valve that opens and closes an intake passage and an exhaust valve that opens and closes an exhaust passage are opened to perform scavenging in the cylinder, and a valve of the exhaust valve. Disclosed is a two-stroke engine having a fixed lift characteristic and having a supercharger in the intake passage, which is rotationally driven by the rotation of the crankshaft and composed of a Roots blower (two-stroke engine with a supercharger). It is

Further, Patent Literature 1 discloses that a two-stroke engine with a supercharger is provided with a variable valve device for variably controlling the opening/closing valve timing of an intake valve.

JP 2009-036144 A

By the way, when performing compression self-ignition combustion (CI combustion) in which fuel is compressed and self-ignited in a two-stroke engine with a supercharger, similar to a four-stroke engine, the difference in the composition of the fuel used (for example, the fuel is gasoline) There is a problem that the ignitability of the fuel itself varies depending on the amount of ethanol mixed in some cases, and the cetane number when the fuel is light oil, and the self-ignition and combustion of the fuel are not stable.

Regarding this point, it is conceivable to change the closing timing of the intake valve (change the effective compression ratio) according to the ignitability of the fuel. Since the intake valve is open during the compression stroke, the intake air supplied to the combustion chamber is blown back to the intake port, so the required amount of intake air cannot be secured, resulting in a decrease in engine torque. There is

The present invention has been made in view of this point, and its object is to obtain stable self-ignition and combustion of fuel regardless of the ignitability of the fuel itself, while suppressing changes in engine torque. To provide a supercharged two-stroke engine capable of

In order to achieve the above object, the present invention provides a cylinder forming a combustion chamber, a piston inserted into the cylinder, an intake valve and an exhaust valve disposed above the cylinder and opening and closing an intake port and an exhaust port, respectively. valves, and a supercharger provided in an intake passage connected to the engine body. A variable valve mechanism capable of changing timing and valve closing timing, ignitability estimation means for estimating ignitability of the fuel supplied to the combustion chamber, and control means for controlling the operation of the variable valve mechanism. The opening period of the intake valve and the exhaust valve is such that the opening timing of the intake valve is later than the opening timing of the exhaust valve, and the closing timing of the intake valve is the above timing. The variable valve mechanism is set to satisfy a specific condition that the closing timing of the exhaust valve is substantially the same as or later than the closing timing of the exhaust valve. A valve mechanism that interlocks and changes both the valve opening timing and the valve closing timing while keeping the valve period constant, and the control means operates in a low load operating region in which the engine load of the engine main body is lower than a predetermined load. In, the fuel is configured to perform compression ignition combustion, and the turbocharger operates when the operating state of the engine body is in a compression ignition combustion region in which the fuel is subjected to compression ignition combustion. Further, when the operating state of the engine body is in the compression ignition combustion region, the lower the ignitability estimated by the ignitability estimating means, the lower the ignitability, the intake valve and the exhaust valve The valve opening timing and valve closing timing are advanced so that the effective compression ratio of the engine body is higher and the scavenging pressure in the scavenging stroke is lower than when the ignitability is high while the above specific conditions are satisfied. In order to turn the angle, it is configured to operate the variable valve mechanism.

With the above configuration, when the ignitability estimated by the ignitability estimating means is low, the closing timing of the intake valve is advanced (the effective compression ratio is increased), so that the combustion chamber at compression top dead center The compression end temperature, which is the gas temperature of On the other hand, when the ignitability estimated by the ignitability estimating means is high, the closing timing of the intake valve is retarded (the effective compression ratio is lowered), thereby lowering the compression end temperature. Therefore, self-ignition and combustion of the fuel can be stabilized regardless of the ignitability of the fuel itself.

Here, in a two-stroke engine with a supercharger, when the closing timing of the intake valve is retarded, the position of the piston at the start of compression is closer to the top dead center of the compression stroke, resulting in a lower effective compression ratio. On the other hand, by supplying the intake air supercharged by the turbocharger into the combustion chamber, even if the intake valve is open when the piston is moving toward compression top dead center, the intake air is supplied into the combustion chamber. No intake air is blown back into the intake port. Therefore, by retarding the closing timing of the intake valve, the effective compression ratio can be lowered while keeping the intake air amount constant. Further, when the closing timing of the intake valve is advanced, the position of the piston at the start of compression is further removed from the compression top dead center, increasing the effective compression ratio. During this advance angle as well, the intake air amount can be kept constant as in the case of retardation. As a result, whether the closing timing of the intake valve is advanced or retarded, the necessary engine torque can be secured without changing the engine torque.

In one embodiment of the supercharged two-stroke engine, the fuel includes gasoline, and the ignitability estimating means estimates a mixing ratio of ethanol to the gasoline, and the estimated mixing ratio of ethanol is high. It is configured to estimate that the ignitability of the fuel is as low as possible.

As a result, the ignitability of the fuel (gasoline) itself can be accurately estimated from the mixing ratio of ethanol to gasoline.

In another embodiment of the supercharged two-stroke engine, the fuel includes light oil, and the ignitability estimation means estimates a cetane number of the light oil, and the lower the estimated cetane number, the higher the It is configured to estimate that the ignitability of the fuel is low.

As a result, the ignitability of the fuel (light oil) itself can be accurately estimated from the cetane number of the light oil.

In still another embodiment of the two-stroke engine with a supercharger, an outside air temperature detecting means for detecting an outside air temperature, an engine water temperature detecting means for detecting a temperature of engine cooling water in the engine body, and an engine in the engine body oil temperature detection means for detecting the temperature of oil; and when the operating state of the engine body is in the compression ignition combustion region, the outside air temperature detection means, the engine water temperature detection means, and the oil temperature detection means, respectively. Based on the detection result and the effective compression ratio of the engine body when it is assumed that the valve closing timing of the intake valve and the exhaust valve is changed by the variable valve mechanism according to the ignitability of the fuel, Compression end temperature estimating means for estimating a compression end temperature, which is a gas temperature in the combustion chamber at top dead center, the control means, when the operating state of the engine body is in the compression self-ignition combustion region , in addition to the ignitability estimated by the ignitability estimating means, the compression end temperature estimated by the compression end temperature estimating means is taken into account to operate the variable valve mechanism; When the compression end temperature estimated by the compression end temperature estimating means exceeds a predetermined temperature range, which is a temperature range in which self-ignition and combustion of fuel are possible, the control means adjusts the intake valve set based on the ignitability. and correcting the valve opening timing and valve closing timing of the exhaust valve to the retard side from the set valve opening timing and valve closing timing within the range that satisfies the specific condition, while estimating by the compression end temperature estimating means When the compression end temperature obtained is below the predetermined temperature range, the valve opening timing and the valve closing timing of the intake valve and the exhaust valve set based on the ignitability are set within a range that satisfies the specific condition. It is configured to correct the valve opening timing and the valve closing timing to the advance side.

As a result, in addition to the ignitability estimated by the ignitability estimating means, the compression end temperature estimated by the compression end temperature estimating means (hereinafter referred to as the estimated compression end temperature) is taken into account to operate the variable valve mechanism. Therefore, self-ignition and combustion of the fuel can be further stabilized. That is, when the estimated compression end temperature is within a predetermined temperature range (an appropriate temperature range for fuel ignitability (a temperature range in which fuel self-ignition and combustion are performed appropriately)), the ignitability estimation means At least the valve closing timing of the intake valve or at least the valve closing timings of the intake valve and the exhaust valve are changed using at least the amount of change in the valve closing timing corresponding to the estimated ignitability. On the other hand, when the estimated compression end temperature exceeds the predetermined temperature range, the change amount is corrected to the retard side, and the change amount after the correction is used to determine at least the closing timing of the intake valve, or the intake valve. And at least the closing timing of the exhaust valve is changed. Further, when the estimated compression end temperature falls below the predetermined temperature range, the change amount is corrected to the advance side, and the change amount after the correction is used to determine at least the closing timing of the intake valve, or the intake valve. And at least the closing timing of the exhaust valve is changed. As a result, self-ignition and combustion of fuel can be further stabilized.

As described above, according to the supercharged two-stroke engine of the present invention, when the operating state of the engine body is in the compression ignition combustion region, the lower the ignitability estimated by the ignitability estimating means, the higher the intake air. By advancing at least the closing timing of the valves or at least the closing timing of the intake and exhaust valves so as to increase the effective compression ratio of the engine body, while suppressing changes in engine torque, Self-ignition and combustion of the fuel can be stabilized regardless of the ignitability of the fuel itself. Therefore, in a two-stroke engine with a supercharger that performs compression self-ignition combustion, it is possible to obtain high combustion stability and appropriate engine torque, suppress abnormal combustion, and suppress deterioration of emission performance.

1 is a schematic configuration diagram of a two-stroke engine with a supercharger according to an embodiment of the present invention; FIG. It is a schematic diagram showing a connection relationship between a mechanical supercharger and a two-stroke engine with a supercharger. FIG. 2 is a block diagram showing a control system of the supercharged two-stroke engine; 4 is a performance curve graph showing the characteristics of the compressor of the mechanical supercharger; FIG. 3 is a diagram showing an example of lift characteristics (here, referred to as basic lift characteristics) of an intake valve and an exhaust valve; FIG. 4 is a diagram showing a state inside a cylinder during a scavenging stroke, showing a state in which only an exhaust valve is open; FIG. 4 is a diagram showing a state inside a cylinder during a scavenging stroke, showing a state in which both the intake valve and the exhaust valve are open; FIG. 4 is a diagram showing lift characteristics when closing timings of an intake valve and an exhaust valve are advanced from basic lift characteristics; FIG. 5 is a diagram showing lift characteristics when the valve closing timing of only the intake valve is retarded from the basic lift characteristics; 4 is a graph showing changes in compression end temperature when the intake valve and/or the exhaust valve are retarded or advanced. 4 is a graph showing changes in engine torque when retarding or advancing intake valves and/or exhaust valves; FIG. 4 is a diagram showing a state inside a cylinder when only intake valves are open; FIG. 4 is a diagram showing a state inside a cylinder when closing timings of an intake valve and an exhaust valve are advanced; Processing operation of the ECU when the closing timing of the intake valve and the exhaust valve is retarded or advanced based on the ignitability of the fuel and the estimated compression end temperature when the operating state of the engine body is in the compression self-ignition combustion region. is a flow chart showing a part of. 4 is a flow chart showing the rest of the processing operation of the ECU;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a supercharged two-stroke engine 1 (hereinafter abbreviated as engine 1) according to an embodiment of the present invention. This engine 1 is an engine mounted on a vehicle, and is a gasoline engine supplied with a fuel containing gasoline (which may contain ethanol) in this embodiment.

The engine 1 includes an engine body 10. The engine body 10 includes a cylinder block 12 provided with a plurality of cylinders 11 (only one is shown in FIG. 1), and a cylinder block 12 provided on the cylinder block 12. and a cylinder head 13 . The plurality of cylinders 11 are arranged such that the cylinder axis direction is the vertical direction, and the direction perpendicular to the paper surface direction is the cylinder row direction. A piston 15 is fitted in each cylinder 11 of the engine body 10 so as to be reciprocally slidable. The combustion chamber 16 is a so-called pent roof type combustion chamber 16, and the wall surface forming the combustion chamber 16 in the cylinder head 13 has two inclined surfaces 13a and 13b. The piston 15 is connected via a connecting rod 17 in the cylinder block 12 to a crankshaft 18 extending in the cylinder row direction. A water jacket 12a through which engine cooling water flows is formed around the cylinder 11 in the cylinder block 12 .

The engine body 10 has a so-called overhead camshaft type valve mechanism, and the cylinder head 13 is provided with an intake port 19 and an exhaust port 20 communicating with the combustion chamber 16 for each cylinder 11 . Each intake port 19 is provided with an intake valve 21 for opening and closing the opening of each intake port 19 on the side of the combustion chamber 16 . Each exhaust port 20 is provided with an exhaust valve 22 for opening and closing the opening of each exhaust port 20 on the side of the combustion chamber 16 . The intake valve 21 and the exhaust valve 22 for each cylinder 11 are arranged above the cylinder 11 . The opening of each intake port 19 on the side of the combustion chamber 16 is formed in one of the two inclined surfaces 13a and 13b of the cylinder head 13 (hereinafter referred to as the intake-side inclined surface 13a). The 16-side opening is formed in the other of the two inclined surfaces 13a and 13b of the cylinder head 13 (hereinafter referred to as the exhaust-side inclined surface 13b).

The intake port 19 is connected to an intake passage 50 which will be described later. As shown in FIG. 1, the intake port 19 extends in a direction perpendicular to both the central axis direction of the cylinder 11 and the row direction of the cylinders (hereinafter referred to as the engine width direction) from the connection portion with the intake passage 50 in the cylinder head 13. ), extends toward the cylinder block 12 side toward the other side in the engine width direction with a slight inclination, and then near the combustion chamber 16 toward the one side in the engine width direction. curved and elongated. As shown in FIGS. 6 and 7, a stepped portion 13c is formed at the boundary between the intake-side inclined surface 13a and the exhaust-side inclined surface 13b. Although details will be described later, this stepped portion 13 c is a portion for suppressing the flow of intake air, which flows from the intake port 19 into the combustion chamber 16 , toward the exhaust port 20 .

On the other hand, the exhaust port 20 is connected to an exhaust passage 60 which will be described later. As shown in FIG. 1, the exhaust port 20 slightly extends from the opening on the side of the combustion chamber 16 toward the side opposite to the cylinder block 12, and then extends straight toward the one side in the engine width direction. there is

In the cylinder head 13, an intake camshaft 31 for operating each intake valve 21 and an exhaust camshaft 41 for operating each exhaust valve 20 are provided so as to extend in the axial direction of the crankshaft 18 (in the direction of the row of cylinders). It is Each camshaft 31, 41 is connected to the crankshaft 18 via a power transmission mechanism such as a chain/sprocket mechanism (not shown). As a result, each camshaft 31 , 41 rotates in conjunction with the rotation of the crankshaft 18 .

The intake camshaft 31 is attached with an intake variable valve mechanism that varies the valve timing. In this embodiment, the variable intake valve mechanism has an electric intake S-VT (Sequential-Valve Timing) 30 . The electric intake S-VT 30 is configured to continuously change the rotation phase of the intake camshaft 31 within a predetermined angle range. In other words, the electric intake S-VT 30 is a phase-type variable valve mechanism that changes both the valve-opening timing and the valve-closing timing while keeping the valve-opening period constant. The opening timing and closing timing of the intake valve 21 are continuously changed by the electric intake S-VT 30 . The intake variable valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

The exhaust camshaft 41 is also attached with an exhaust variable valve mechanism that varies the valve timing. In this embodiment, the exhaust variable valve mechanism has an electric exhaust S-VT40. The electric exhaust S-VT 40 is configured to continuously change the rotation phase of the exhaust camshaft 41 within a predetermined angle range. In other words, the electric exhaust S-VT 40 is a phase-type variable valve mechanism, and changes both the valve opening timing and the valve closing timing while keeping the valve opening period constant. Due to this electric exhaust S-VT 40, the opening timing and closing timing of the exhaust valve 22 are continuously changed. The exhaust variable valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

As shown in FIG. 1 , the cylinder head 13 is provided with a fuel injection valve 23 for directly injecting fuel into the combustion chamber 16 for each cylinder 11 . The fuel injection valve 23 is arranged such that its injection port faces the interior of the combustion chamber 16 from the ceiling of the combustion chamber 16 . The fuel injection valve 23 receives a control signal from the ECU 100, which will be described later, and performs injection at an injection timing (after both the intake valve 21 and the exhaust valve 22 are closed) set according to the operating state of the engine body 10 in the compression stroke. In addition, an amount of fuel corresponding to the operating state of the engine body 10 is directly injected into the combustion chamber 16 . A fuel injection valve that injects fuel into the intake port 19 may be provided instead of or in addition to the fuel injection valve 23 .

A spark plug 24 is attached to the cylinder head 13 for each cylinder 11 to burn the fuel injected into the cylinder 11 by spark ignition. As shown in FIG. 1, the spark plug 24 is arranged so as to face the inside of the combustion chamber 16 from one side (the exhaust side in this embodiment) of the cylinder head 13 . The ignition plug 24 receives a control signal from the ECU 100 and energizes the electrode 24a so as to generate sparks at desired ignition timing.

As shown in FIG. 1 , an intake passage 50 is connected to the surface of the engine main body 10 on the other side in the engine width direction so as to communicate with the intake port 19 of each cylinder 11 . On the other hand, the one side surface of the engine body 10 in the engine width direction is connected so as to communicate with the exhaust port 20 of each cylinder 11, and exhausts the burned gas (that is, exhaust gas) from each cylinder 11. An exhaust passage 60 is connected.

An air cleaner (not shown) for filtering intake air is provided at the upstream end of the intake passage 50 . On the other hand, a surge tank 52 is arranged near the downstream end of the intake passage 50 . The intake passage 50 on the downstream side of the surge tank 52 is an independent intake passage that branches for each cylinder 11 , and the downstream end of each independent intake passage is connected to the intake port 19 of each cylinder 11 .

A mechanical supercharger 53 is arranged between the air cleaner and the surge tank 52 in the intake passage 50 . In the following description, a portion of the intake passage 50 on the upstream side of the mechanical supercharger 53 is referred to as an upstream intake passage 50a (see FIG. 2). The side portion is referred to as a downstream intake passage 50b.

The mechanical supercharger 53 is a supercharger that does not use exhaust energy, and more specifically, is a supercharger that is rotationally driven by rotation of a crankshaft 18 provided in the engine body 10 . As shown in FIG. 2, the mechanical supercharger 53 and the crankshaft 18 are connected by a first pulley 71, a second pulley 72, and a belt 73 connecting the first pulley 71 and the second pulley 72. It is Specifically, a first pulley 71 is attached to the output shaft 18a of the crankshaft 18, and a second pulley 72 is attached to the input shaft 53b of the compressor 53a (constituted by a centrifugal blower) of the mechanical supercharger 53. installed. 2, the surge tank 52 and the exhaust passage 60 are omitted.

Since the mechanical supercharger 53 is rotationally driven by the rotation of the crankshaft 18, its rotational speed is proportional to the rotational speed of the crankshaft 18 (that is, the rotational speed of the engine body 10). The respective diameters of the first and second pulleys 71 and 72 are set so that the number of rotations of the compressor 53a becomes a desired number of rotations. An electromagnetic clutch may be arranged between the second pulley 72 and the input shaft 53b so that the rotation speed of the compressor 53a can be adjusted.

In this embodiment, the mechanical supercharger 53 operates in all operating regions of the engine body 10 (low-load operating region and high-load operating region described later). Incidentally, instead of the mechanical supercharger 53, an electric supercharger having a centrifugal blower as a compressor may be used. 10 may be in the compression ignition combustion region, which will be described later. However, like the mechanical supercharger 53, the electric supercharger is preferably operated in the entire operating range of the engine body 10 as well.

The upstream portion of the exhaust passage 60 is constituted by an exhaust manifold having an independent exhaust passage branched for each cylinder 11 and connected to the outer end of the exhaust port 20, and a gathering portion where the independent exhaust passages gather. ing.

An exhaust purification catalyst 61 is arranged downstream of the exhaust manifold in the exhaust passage 60 . The exhaust gas purifying catalyst 61 is an oxidation catalyst that promotes reactions in which CO and HC in the exhaust gas are oxidized to produce _CO2 and _H2O . Although not shown, fine particles such as soot contained in the exhaust gas from the combustion chamber 16 of the engine body 10 are present in a portion of the exhaust passage 60 downstream of the exhaust purification catalyst 61. A particulate filter is provided to collect the particles. In this embodiment, the engine 1 does not include a catalyst for removing NOx, but may include a catalyst for removing NOx.

As shown in FIG. 3 , the engine 1 (engine body 10 ) is controlled by an ECU (Engine Control Unit) 100 . The ECU 100 is a well-known microcomputer-based controller. The ECU 100 includes a CPU 101, a memory 102, an input/output bus 103, and the like. The CPU 101 is a central processing unit that executes computer programs (including basic control programs such as an OS, and application programs that are started on the OS and implement specific functions). The memory 102 is composed of RAM and ROM. The ROM contains various computer programs (especially a control program for controlling the engine 1), a combustion range map, an ignitability index map, a change amount map, a temperature range map, and a correction, which are used when executing the computer program. Data including maps are stored. The RAM is a memory provided with a processing area used when the CPU 101 performs a series of processes. The input/output bus 103 inputs and outputs electrical signals to and from the ECU 100 .

The ECU 100 includes a crank angle sensor SN1, an airflow sensor SN2, an accelerator opening sensor SN3, an intake air temperature sensor SN4, an engine water temperature sensor SN5 (engine water temperature detection means), an oil temperature sensor SN6 (oil temperature detection means), and a linear _O2 sensor. Various sensors such as SN7 are electrically connected. Crank angle sensor SN1 is provided in cylinder block 12 and detects the rotation angle of crankshaft 18 . The airflow sensor SN2 detects the flow rate of intake air through the upstream side intake passage 50a. The accelerator opening sensor SN3 is attached to the accelerator pedal mechanism of the vehicle and detects the accelerator opening corresponding to the amount of operation of the accelerator pedal. An intake air temperature sensor SN4 detects the temperature of intake air in the upstream intake passage 50a. Since the outside air temperature can be estimated from this intake air temperature, the intake air temperature sensor SN4 constitutes outside air temperature detection means. The engine water temperature sensor SN5 detects the temperature of engine cooling water flowing through the water jacket 12a. An oil temperature sensor NS6 detects the temperature of engine oil. The linear _O2 sensor SN7 is provided in the exhaust passage 60 between the exhaust manifold and the exhaust purification catalyst 61, and detects the oxygen concentration (air-fuel ratio) in the exhaust gas. These sensors SN1 to SN7 and the like output detection signals to the ECU 100. FIG.

The ECU 100 calculates the rotation speed of the engine body 10 (hereinafter referred to as engine rotation speed) from the detection result of the crank angle sensor SN1. The ECU 100 calculates the load of the engine body 10 (hereinafter referred to as engine load) from the detection result of the accelerator opening sensor SN3.

The ECU 100 determines the operating state of the engine body 10 based on the input signals from the sensors SN1 to SN7, etc. A control signal is output to each device of the engine 1 to control each device. The ECU 100 constitutes control means for controlling the operations of the intake variable valve mechanism and the exhaust variable valve mechanism.

FIG. 4 shows the performance characteristics of the compressor 53a of the mechanical supercharger 53. As shown in FIG. The vertical axis is the ratio of the pressure in the downstream side intake passage 50b to the pressure in the upstream side intake passage 50a (hereinafter simply referred to as pressure ratio), and the horizontal axis is the discharge flow rate from the compressor 53a. In FIG. 4, curve RL represents a rotation limit line, and line SL (substantially straight line) represents a surge line. The area surrounded by these lines is the operable area of the mechanical supercharger 53 . The operating efficiency of the mechanical supercharger 53 increases as the operating point is located closer to the center of the operable region. In this embodiment, the pressure in the upstream side intake passage 50a is basically atmospheric pressure, so the pressure ratio indicates the level of the supercharging pressure by the mechanical supercharger 53. there is

A plurality of curves RSL shown in the operable region are lines connecting operation points where the rotation speed of the compressor 53a is equal, and the closer to the rotation limit line RL, the higher the rotation speed. A dashed-dotted line BL extending vertically across the operable region of the mechanical supercharger 53 is a line connecting the operating points at which the operating efficiency of the compressor 53a is highest for each rotation speed of the compressor 53a. .

Since the compressor 53a is composed of a centrifugal blower, the compressor 53a basically exhibits a tendency such that the higher the rotational speed of the compressor 53a, the larger the pressure ratio and the larger the discharge flow rate. This indicates that the higher the engine speed, the higher the boost pressure. When the engine speed is low, the intake valve 21 and the exhaust valve 22 are opened for a long time per combustion cycle of the engine body 10, so even if the supercharging pressure is low, the exhaust gas can be scavenged. . On the other hand, when the engine speed is high, the actual opening time of the intake valve 21 and the exhaust valve 22 per one combustion cycle of the engine body 10 is short, so the intake air is injected into the combustion chamber 16 at the highest possible supercharging pressure. It is necessary to introduce it and scavenge the exhaust gas at an early stage. For this reason, the compressor 53a having the above-described characteristics enables appropriate scavenging of the exhaust gas.

The boost pressure and flow rate of the intake air to be supplied to the combustion chamber 16 for efficient scavenging of the exhaust gas can be obtained in advance from the engine specifications of the engine body 10 (volume of the combustion chamber 16, etc.). For this reason, in the present embodiment, the required supercharging pressure and intake flow rate are calculated based on the engine specifications of the engine body 10, and the mechanical supercharger such that the operating point is located on the broken line BL 53 is selected. This enables efficient supercharging in accordance with the engine speed.

In this embodiment, depending on the operating state of the engine body 10, compression self-ignition combustion (CI combustion) in which fuel is compressed and self-ignited in the combustion chamber 16 without activating the spark plug 24, and combustion in the combustion chamber by the spark plug 24 16, spark ignition combustion (SI combustion) is performed in which fuel is spark-ignited. Here, "compression ignition" includes SPCCI (Spark Controlled Compression Ignition) combustion in which compression ignition is performed after ignition is assisted by the spark plug 24 .

In this embodiment, the ROM of the memory 102 stores a combustion region map represented by a two-axis coordinate system of engine speed and engine load. In this combustion region map, a low load side operating region in which the engine load is lower than a predetermined load is defined as a compression ignition combustion region, and a high load side operating region in which the engine load is equal to or higher than the predetermined load is defined as a spark ignition combustion region. It is The predetermined load changes according to the engine speed (for example, the higher the engine speed, the higher the predetermined load). However, the predetermined load may be constant regardless of the engine speed. Note that the entire operating range of the engine body 10 may be the compression ignition combustion range.

FIG. 5 shows an example of lift characteristics of the intake valve 21 and the exhaust valve 22. As shown in FIG. The horizontal axis is the crank angle, where the crank angle at the compression top dead center (TDC) is 0°, the advance side (earlier than the compression top dead center) is indicated by minus, and the retard side (compression The time later than the top dead center) is represented by a plus. In FIG. 5, −360° corresponds to compression top dead center one combustion cycle before.

The valve opening period of the intake valve 21 and the exhaust valve 22 includes the compression bottom dead center (BDC), the opening timing of the intake valve 21 is later than the opening timing of the exhaust valve 22, and the closing timing of the intake valve 21 is It is set so as to satisfy a specific condition that it is substantially the same as the closing timing of the exhaust valve 22 or later than the closing timing of the exhaust valve 22 . That is, the intake valve 21 and the exhaust valve 22 exhibit lift characteristics that satisfy the above specific conditions by the intake and exhaust camshafts 31 and 41, the electric intake S-VT 30 and the electric exhaust S-VT 40. there is In the present embodiment, the closing timing of the intake valve 21 and the exhaust valve 22 is defined as the point of 1 mm lift (the point of time near the boundary between the ramp portion and the lift portion). In addition, the opening timing of the intake valve 21 and the exhaust valve 22 is also defined as the point of 1 mm lift (the point of time near the boundary between the ramp portion and the lift portion).

In this embodiment, the lift characteristics shown in FIG. 5 are called basic lift characteristics. In this basic lift characteristic, the opening timing of the intake valve 21 is about 20 degrees crank angle later than the opening timing of the exhaust valve 22, and the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22. It is Here, "the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22" means that the closing timing of the intake valve 21 is slightly earlier than the closing timing of the exhaust valve 22, and It includes both cases where the closing timing of the intake valve 21 is slightly later than the closing timing of the exhaust valve 22 . That is, "the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22" means that the difference between the closing timing of the intake valve 21 and the closing timing of the exhaust valve 22 is 2° to 2° in crank angle. It refers to the case where the angle is about 3°. In this embodiment, the closing timing of the intake valve 21 is slightly later than the closing timing of the exhaust valve 22 (about 2° to 3° in terms of crank angle) in the basic lift characteristics.

It should be noted that the basic lift characteristic may be any characteristic as long as it satisfies the above specific conditions. For example, the closing timing of the intake valve 21 may be later than the closing timing of the exhaust valve 22 . In this case, the difference between the closing timing of the intake valve 21 and the closing timing of the exhaust valve 22 is larger than the difference when the closing timing of the intake valve 21 and the closing timing of the exhaust valve 22 are substantially the same.

In this embodiment, since the engine 1 is a two-stroke engine, both the intake valve 21 and the exhaust valve 22 are opened, and the exhaust gas in the combustion chamber 16 is exhausted by the intake air flowing into the combustion chamber 16 from the intake port 19. There is a scavenging stroke that sweeps into port 20 . When entering the scavenging stroke in the combustion cycle of the engine body 10, the exhaust valve 22 opens earlier than the intake valve 21, as described above. This is to prevent exhaust gas from flowing into the intake port 21 .

Here, FIGS. 6 and 7 illustrate the state inside the combustion chamber 16 during the scavenging stroke.

As shown in FIG. 6, after the fuel burns in the combustion cycle one combustion cycle before, only the exhaust valve 22 is first opened. At this time, the exhaust gas flows toward the exhaust port 20 while the piston 15 descends. Even if the piston 15 is lowered, the exhaust gas flows into the exhaust port 20 due to the combustion pressure.

Next, as shown in FIG. 7, in addition to the exhaust valve 22, the intake valve 21 is opened. When the intake valve 21 is opened, intake air is supplied from the intake port 19 to the combustion chamber 16 . At this time, since the stepped portion 13 c is formed in the cylinder head 13 , the intake air does not flow toward the exhaust port 20 , but mainly flows from the exhaust port 20 in the gap between the intake valve 21 and the cylinder head 13 . Combustion chamber 16 is fed from the far side. By supplying the intake air to the combustion chamber 16 in this manner, the exhaust gas in the combustion chamber 16 is scavenged to the exhaust port 20 by the intake air, as shown in FIG.

Further, as shown in FIGS. 5 and 7, in the first half when the piston 15 is rising toward the compression top dead center, the exhaust valve 22 is opened in addition to the intake valve 21 . As a result, the exhaust gas in the combustion chamber 16 is swept to the exhaust port 20 by the intake air supplied to the combustion chamber 16 and the upward movement of the piston 15 .

Next, while the piston 15 is moving upward, the intake valve 21 and the exhaust valve 22 are closed at approximately the same timing, as shown in FIG. Specifically, in this embodiment, the intake valve 21 is closed with a slight delay after the exhaust valve 22 is closed. After the intake valve 21 is closed, the piston 15 rises to compress the intake air.

In the subsequent compression stroke, fuel is injected into the combustion chamber 16 by the fuel injection valve 23 . In the case of a fuel injection valve that injects fuel into the intake port 19, fuel is injected into the intake port 19 when the intake valve 21 is open.

When the operating state of the engine body 10 is in the compression self-ignition combustion region (low-load side operating region) according to the combustion region map, the fuel is combusted by compression self-ignition near the compression top dead center. On the other hand, when the operating state of the engine body 10 is in the spark ignition combustion region (high load side operating region) according to the combustion region map, the spark plug 24 is operated near the compression top dead center in the compression stroke to ignite the fuel by spark ignition. Burn. In this embodiment, when the engine water temperature detected by the engine water temperature sensor SN5 is lower than a preset temperature, spark ignition combustion is performed without using the combustion region map.

Here, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the ignitability of the fuel itself varies depending on the mixing ratio of ethanol to the fuel (gasoline), and the self-ignition and combustion of the fuel are prevented. I have a problem with instability.

Therefore, in the present embodiment, when the operating state of the engine body 10 is in the compression ignition combustion region, the ECU 100 estimates the ignitability of the fuel supplied to the combustion chamber 16 and adjusts the intake air according to the ignitability. In order to change at least the closing timing of the valve 21 or at least the closing timings of the intake valve 21 and the exhaust valve 22 (to change the effective compression ratio of the engine body 10), the electric intake S-VT 30 and the electric exhaust S- Activate VT40. In this embodiment, both the electric intake S-VT 30 and the electric exhaust S-VT 40 are phase type, so when the valve closing timing changes, the valve opening timing also changes accordingly. Further, in this embodiment, the closing timing (and the opening timing) of both the intake valve 21 and the exhaust valve 22 are changed by the same amount.

In the present embodiment, the ECU 100 estimates the mixing ratio of ethanol in gasoline (the ethanol concentration of the fuel) based on the detection result of the linear _O2 sensor SN7, and the higher the estimated mixing ratio of ethanol, the more fuel is consumed. It is estimated that the ignitability is low. Thus, the ECU 100 and the linear _O2 sensor SN7 constitute ignitability estimation means for estimating the ignitability of the fuel.

Regarding the ignitability of the fuel, an index value obtained by indexing the ignitability is used, and the higher the ethanol concentration, the smaller the index value. The relationship between the ethanol concentration and the index value is predetermined as an ignitability index map (stored in ROM of memory 102).

The theoretical air-fuel ratio of ethanol (9.0) is smaller than the theoretical air-fuel ratio of gasoline (14.7), and the higher the ethanol concentration of fuel, the richer the theoretical air-fuel ratio becomes (that is, the smaller the value). Therefore, when the engine main body 10 is operated at the theoretical air-fuel ratio of the expected ethanol concentration, and there is residual oxygen in the exhaust gas, it is determined that the ethanol concentration of the fuel is higher than expected. can do. Therefore, from the detection signal of the linear _O2 sensor SN7, the ECU 100 determines that there is little ethanol in the fuel when the air-fuel ratio is lean, and determines that there is much ethanol in the fuel when the air-fuel ratio is rich. to estimate the ethanol concentration of the fuel. The ethanol concentration is estimated when the temperature detected by the engine coolant temperature sensor SN5 or the oil temperature sensor SN6 is equal to or higher than a predetermined temperature. This predetermined temperature is a temperature at which ethanol supplied into the combustion chamber 16 is generally vaporized. Estimation of the ethanol concentration can basically be performed each time the fuel tank is refueled (for example, determined from the detected value of the level gauge sensor of the fuel tank). The estimated ethanol concentration may be stored in the RAM of memory 102 until the next refueling, and the stored value may be used.

When the operating state of the engine body 10 is in the compression ignition combustion region, the ECU 100 adjusts the closing timings of the intake valve 21 and the exhaust valve 22 as the estimated ignitability is lower (the index value is smaller). , the electric intake S-VT 30 and the electric exhaust S-VT 40 are operated in order to advance the effective compression ratio of the engine body 10 while satisfying the above specific conditions.

In this embodiment, the lift characteristics of the intake valve 21 and the exhaust valve 22 are defined as the basic lift characteristics shown in FIG. 5 when the index value is a value corresponding to the ethanol concentration of the fuel being 0%. As the index value becomes smaller from the value corresponding to the ethanol concentration of 0%, the closing timings of the intake valve 21 and the exhaust valve 22 are adjusted based on the operation of the electric intake S-VT 30 and the electric exhaust S-VT 40. The lift characteristic (indicated by the dashed line) is advanced (the closing timing of the exhaust valve 22 is also advanced in order to satisfy the specific condition (see FIG. 8)). In this embodiment, the amount of change in the closing timings of the intake valve 21 and the exhaust valve 22 (advance amount from the basic lift characteristic) is the same. The relationship between the index value and the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22 (advance amount from the basic lift characteristic) is determined in advance as a change amount map (stored in the ROM of the memory 102). ing.

In this way, the valve closing timings of the intake valve 21 and the exhaust valve 22 may be changed according to the ignitability of the fuel itself. When in the region, the closing timings of the intake valve 21 and the exhaust valve 22 are changed in consideration of the compression end temperature estimated as described later in addition to the estimated ignitability.

When the operating state of the engine body 10 is in the compression ignition combustion region, the ECU 100 detects the outside air temperature estimated from the detection result of the intake air temperature sensor SN4, the detection result of the engine coolant temperature sensor SN5, and the detection result of the oil temperature sensor SN6. and changing the valve closing timing of the intake valve 21 and the exhaust valve 22 according to the ignitability of the fuel (the valve closing timing is changed by the amount of change obtained from the index value and the amount of change map). Based on the assumed effective compression ratio of the engine body 10, the compression end temperature, which is the temperature of the gas in the combustion chamber 16 at the compression top dead center, is estimated. Therefore, the ECU 100 constitutes compression end temperature estimating means for estimating the compression end temperature.

When estimating the compression end temperature, in addition to the detection results of the sensors SN4 to SN6 and the effective compression ratio, the engine speed calculated from the detection results of the crank angle sensor SN1 may also be taken into consideration. That is, the compression end temperature is low at low rotation speeds where the compression stroke time is long, and the compression end temperature is high at high rotation speeds where the compression stroke time is short. At high engine speeds, the time required for the scavenging stroke is shortened, so the boost pressure is increased, and this increase in boost pressure raises the intake air temperature and the compression end temperature. Alternatively, the compression end temperature may be estimated based on the outside air temperature and the effective compression ratio (or, in addition to these, the engine speed).

Then, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the ECU 100 determines that the compression end temperature estimated as described above (hereinafter, estimated compression end temperature) is within a predetermined temperature range. , the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22 according to the estimated ignitability (index value) (the amount of change determined from the index value and the change amount map), the intake valve 21 and the exhaust valve 22 are changed. The predetermined temperature range is a temperature range appropriate for the ignitability of fuel (a temperature range in which self-ignition and combustion of fuel are appropriately performed). The predetermined temperature range becomes a higher temperature range as the ignitability of the fuel is lower (as the index value is smaller). The predetermined temperature range corresponding to the ignitability when the ethanol concentration of the fuel is 0% is, for example, the range of 1000K±20K. The relationship between the index value and the predetermined temperature range is determined in advance as a temperature range map (stored in ROM of memory 102).

On the other hand, if the estimated compression end temperature exceeds the predetermined temperature range when the operating state of the engine body 10 is in the compression ignition combustion region, the ECU 100 corrects the change amount to the retard side. , and the amount of change after the correction), the closing timings of the intake valve 21 and the exhaust valve 22 are changed. The amount of correction to the retardation side is increased as the estimated compression end temperature exceeds the maximum value of the predetermined temperature range. Further, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the ECU 100 corrects the change amount to the advance side when the estimated compression end temperature is below the predetermined temperature range. , the closing timings of the intake valve 21 and the exhaust valve 22 are changed by the corrected change amount. The amount of correction to the advance angle side is increased as the amount by which the estimated compression end temperature falls below the minimum value of the predetermined temperature range increases. That is, the estimated compression when it is assumed that the closing timings of the intake valve 21 and the exhaust valve 22 are changed (the effective compression ratio is further changed by the correction) with the change amount after the correction to the retard side or the advance side. The end temperature is kept within the predetermined temperature range. The relationship between the amount of excess and the amount of correction to the retard side, and the relationship between the amount of decrease and the amount of correction to the advance side, are determined in advance as a correction map (stored in the ROM of memory 102). ing. When the closing timings of the intake valve 21 and the exhaust valve 22 are changed using the corrected change amount in this way, the above specific condition is also satisfied. In this embodiment, the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22 even after the change.

When the closing timings of the intake valve 21 and the exhaust valve 22 are changed by the amount of change after the correction to the retard side, the closing timings of the intake valve 21 and the exhaust valve 22 are retarded from the basic lift characteristics. Sometimes. In this case, instead of retarding the closing timings of the intake valve 21 and the exhaust valve 22, as shown in FIG. good too. Further, when the basic lift characteristic is a characteristic in which the closing timing of the intake valve 21 is later than the closing timing of the exhaust valve 22 (the difference between the closing timing of the intake valve 21 and the closing timing of the exhaust valve 22 is When the closing timing of the valve 21 is larger than the difference when the closing timing of the exhaust valve 22 is substantially the same as the closing timing of the exhaust valve 22), when the closing timings of the intake valve 21 and the exhaust valve 22 advance from the basic lift characteristic, Instead of advancing the closing timings of the intake valve 21 and the exhaust valve 22, the closing timing of only the intake valve 21 may be advanced as long as the specific conditions are satisfied.

FIG. 10 shows the result of calculation by simulation of changes in the compression end temperature when the closing timing of the intake valve 21 and/or the exhaust valve 22 is adjusted. Further, FIG. 11 shows the result of calculation by simulation of changes in engine torque (output torque of the engine body 10) when the closing timings of the intake valve 21 and/or the exhaust valve 22 are adjusted. In the simulations of FIGS. 10 and 11, the engine speed is set to 1500 rpm and the air-fuel ratio is set to A/F=30.

In FIG. 10, the vertical axis is the compression end temperature, and the horizontal axis is the amount of change in the closing timing of the intake valve 21 and/or the exhaust valve 22 (the amount of change in the crank angle). The horizontal axis represents the valve closing timing for the basic lift characteristics shown in FIG. In the simulations of FIGS. 10 and 11 as well, when the valve closing timing changes, the valve opening timing changes accordingly. In the graph shown in FIG. 10, the curve with diamond marks indicates the case where the intake valve 21 and the exhaust valve 22 are synchronized and their closing timings are retarded or advanced by the same amount. indicates the case where only the intake valve 21 is retarded or advanced, and the curve with square marks indicates the case where only the exhaust valve 22 is retarded or advanced. The dotted line shown in FIG. 10 represents the median value of the predetermined temperature range corresponding to ignitability when the ethanol concentration of the fuel is 0%. This simulation is based on the condition that the opening timing of the intake valve 21 is not earlier than the opening timing of the exhaust valve 22 . Therefore, the amount of advance when only the intake valve 21 closes is advanced is up to about 20 degrees, and the amount of advance when only the exhaust valve 22 is delayed is also about 20 degrees. °. Also, in this simulation, the closing timing of the exhaust valve 22 is allowed to be later than the closing timing of the intake valve 21 .

In FIG. 11 , the vertical axis is the engine torque, and the horizontal axis is the amount of change in closing timing of the intake valve 21 and/or the exhaust valve 22 . The notation of the horizontal axis and the curves with marks indicating the target of the advance angle and the retardation angle are the same as in FIG.

As shown in FIG. 10, when the intake valve 21 and the exhaust valve 22 are synchronized and the valve closing timing is retarded, the greater the retardation amount, the lower the compression end temperature. Further, it can be seen that the compression end temperature decreases to the same extent as when the intake valve 21 and the exhaust valve 22 are synchronized when the closing timing of only the intake valve 21 is retarded. This is because by retarding the closing timing of the intake valve 21, the position of the piston 15 at the start of compression becomes close to the top dead center of the compression stroke, and the effective compression ratio changes.

On the other hand, it can be seen that the compression end temperature only slightly decreases when the closing timing of only the exhaust valve 21 is retarded. As described above, in this simulation, when the valve closing timing changes, the valve opening timing changes accordingly. By delaying the opening timing of the exhaust valve 22, the exhaust valve 22 is opened when the in-cylinder pressure is low, making it difficult to discharge the exhaust gas. This increases the amount of exhaust gas in the combustion chamber 16 at the start of compression. As a result, even if the exhaust valve 22 is retarded to reduce the effective compression ratio, the compression end temperature is less likely to decrease.

Here, if the closing timing of only the intake valve 21 is retarded, only the intake valve 21 is opened when the piston 15 is at a position near the compression top dead center, as shown in FIG. However, in this embodiment, the intake air is mainly supplied to the combustion chamber 16 from a portion of the gap between the intake valve 21 and the cylinder head 13 that is farther from the exhaust port 20, and substantially, A passage area between the intake port 19 and the combustion chamber 16 is small. The intake air supplied from the intake port 19 to the combustion chamber 16 is supercharged by the mechanical supercharger 53 . For these reasons, in this embodiment, as shown in FIG. 12, even if only the intake valve 21 is open when the piston 15 is rising, supercharged intake air is supplied to the combustion chamber 16. Therefore, almost no air blows back from the combustion chamber 16 to the intake port 19 .

If almost no air is blown back from the combustion chamber 16 to the intake port 19, the amount of intake air supplied to the combustion chamber 16 will be constant. Specifically, if the engine speed is constant and the rotation speed of the compressor 53a of the mechanical supercharger 53 is constant, the discharge flow rate from the mechanical supercharger 53 is constant. If the discharge flow rate from the mechanical supercharger 53 is constant and there is no blowback from the combustion chamber 16 to the intake port 19, the intake air amount supplied to the combustion chamber 16 is constant. Therefore, as shown in FIG. 11, the engine torque hardly changes even when the closing timing of the intake valve 21 is retarded.

On the other hand, referring to FIG. 10, when the closing timings of the intake valve 21 and the exhaust valve 22 are advanced in synchronization with each other, the compression end temperature rises as the advance amount increases. This is because the amount of exhaust gas in the combustion chamber 16 is increased in addition to the effective compression ratio being increased. That is, as shown in FIG. 13, when the intake valve 21 and the exhaust valve 22 are synchronized and the respective closing timings are advanced, the position of the piston 15 moves from a position further away from the compression top dead center to the combustion chamber 16. Compression of the gas inside begins, reducing the effective compression ratio. Further, if the closing timing of the intake valve 21 is advanced, the intake air is supplied to the combustion chamber 16 when the piston 15 is at a position near the compression bottom dead center. The scavenging pressure when scavenging the exhaust gas is low. This suppresses the scavenging of the exhaust gas, so that the amount of exhaust gas in the combustion chamber 16 at the start of compression increases, as shown in FIG.

Further, referring to FIG. 10, when the closing timing of only the intake valve 21 is advanced, the compression end temperature rises. It can be seen that the amount of increase in the edge temperature is small. If the closing timing of only the intake valve 21 is advanced, the closing timing of the exhaust valve 22 becomes later than the closing timing of the intake valve 21, so the effective compression ratio is determined by the closing timing of the exhaust valve 22. When only the intake valve 21 is advanced, the effective compression ratio hardly changes. On the other hand, as described above, the scavenging pressure at the time of scavenging the exhaust gas in the combustion chamber 16 becomes low, and the amount of exhaust gas in the combustion chamber 16 at the start of compression increases. Therefore, even if the closing timing of only the intake valve 21 is advanced, the compression end temperature rises, but compared to the case where the intake valve 21 and the exhaust valve 22 are synchronized, the increase in the compression end temperature is smaller. . Also, it can be seen that when the advance angle amount is 20 degrees, it is almost the same as when the advance angle amount is 10 degrees. This is because the effective compression ratio is determined by the closing timing of the exhaust valve 22, and even if the closing timing of the intake valve 21 is advanced, the effective compression ratio does not change.

Further, referring to FIG. 10, it can be seen that the compression end temperature hardly changes when the closing timing of only the exhaust valve 22 is advanced. This is because even if the closing timing of only the exhaust valve 22 is advanced, the closing timing of the intake valve 21 does not change and the effective compression ratio does not change.

Here, as described above, even if the engine speed is constant and the intake valve 21 is advanced, the amount of intake air supplied to the combustion chamber 16 is constant. Therefore, as shown in FIG. 11, the engine torque hardly changes even when the closing timing of the intake valve 21 is advanced.

As described above, in the present embodiment, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the compression end temperature is adjusted to a temperature range appropriate for fuel ignitability. By correcting the valve closing timings of 21 and exhaust valve 22, it is possible to appropriately perform self-ignition and combustion of fuel while suppressing changes in engine torque.

Next, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the closing timings of the intake valve 21 and the exhaust valve 22 are retarded or advanced based on the ignitability of the fuel and the estimated compression end temperature. The processing operation of the ECU 100 when the engine is turned on will be described with reference to the flow charts of FIGS. 14 and 15. FIG. Processing operations based on this flow chart are executed for each combustion cycle while the engine 1 is operating.

In the first step S1, signals from various sensors are read, and in the next step S2, the ignitability of fuel is estimated. Here, the index value is obtained from the estimated value of the ethanol concentration already stored in the RAM of the memory 102 and the ignitability index map.

In the next step S3, the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22 (advance amount from the basic lift characteristic) is obtained from the index value obtained in step S2 and the change amount map.

In the next step S4, the outside air temperature estimated from the detection result of the intake air temperature sensor SN4, the detection result of the engine water temperature sensor SN5, the detection result of the oil temperature sensor SN6, and the above change amount obtained in step S3, the intake valve The compression end temperature is estimated based on the effective compression ratio of the engine body 10 when it is assumed that the closing timings of 21 and exhaust valve 22 are changed.

In the next step S5, it is determined whether or not the estimated compression end temperature estimated in step S4 is within a predetermined temperature range. When the determination in step S5 is YES, the process proceeds to step S6, and the closing timings of the intake valve 21 and the exhaust valve 22 are changed using the amount of change obtained in step S3.

On the other hand, when the determination in step S5 is NO, the process proceeds to step S7 to determine whether or not the estimated compression end temperature exceeds the predetermined temperature range. When the determination in step S7 is YES, the process proceeds to step S8, and the change amount obtained in step S3 is changed to the retard side. This correction amount is obtained from the excess amount of the estimated compression end temperature with respect to the maximum value of the predetermined temperature range and the correction map.

When the determination in step S7 is NO, the process proceeds to step S9, and the change amount obtained in step S3 is changed to the advance angle side. This correction amount is obtained from the amount by which the estimated compression end temperature falls below the minimum value of the predetermined temperature range and the correction map.

After step S8 or step S9, the process proceeds to step S10 to change the closing timings of the intake valve 21 and the exhaust valve 22 with the changed amount after the correction in step S8 or step S9, and then returns.

Therefore, in the present embodiment, when the operating state of the engine body 10 is in the compression self-ignition combustion region, the lower the ignitability of the fuel, the more the closing timings of the intake valves 21 and the exhaust valves 22 are adjusted to the effectiveness of the engine body 10. By advancing the timing so as to increase the compression ratio, it is possible to stabilize self-ignition and combustion of the fuel, regardless of the ignitability of the fuel itself, while suppressing changes in the engine torque. Therefore, in a two-stroke engine with a supercharger that performs compression self-ignition combustion, it is possible to obtain high combustion stability and appropriate engine torque, suppress abnormal combustion, and suppress deterioration of emission performance.

Further, in the present embodiment, when the operating state of the engine body 10 is in the compression self-ignition combustion region, in addition to the ignitability of the fuel, the estimated compression end temperature is taken into account to -Since the VT 40 is operated (corrects the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22 according to the ignitability (index value)), self-ignition and combustion of fuel are further stabilized. can be done.

The present invention is not limited to the above embodiments, and substitutions are possible without departing from the scope of the claims.

For example, in the above embodiment, both the intake variable valve mechanism and the exhaust variable valve mechanism are of the phase type. are retarded or advanced at the same time. It may be configured such that only the valve closing timing can be retarded or advanced.

Further, in the above embodiment, the engine 1 is a gasoline engine, but it may be a diesel engine supplied with fuel containing light oil. In this case, the entire operating region of the engine body 10 becomes the compression ignition combustion region. Further, there is no need to provide an ignition plug in the cylinder block 13, and the injection timing of the fuel from the fuel injection valve 23 is set near compression top dead center in the compression stroke.

When the engine 1 is a diesel engine supplied with fuel containing light oil, the ECU 100 estimates the cetane number of the light oil, and estimates that the lower the estimated cetane number, the lower the ignitability of the fuel. The cetane number of light oil is estimated from the result of comparison between a reference ignition timing set based on fuel having an average cetane number (eg, 47) and the actual ignition timing. The actual ignition timing is the crank angle position at which the pressure change rate dP/dθ indicates the peak position, where θ is the crank angle and P is the in-cylinder pressure (detected by the in-cylinder pressure sensor). Thus, the cetane number of the fuel is estimated based on the actual ignition timing of the fuel injected from the fuel injection valve 23, and the ignitability (index value) is estimated from the cetane number. As in the case of gasoline, the ECU 100 changes the closing timings of the intake valve 21 and the exhaust valve 22 in consideration of the estimated compression end temperature in addition to the estimated ignitability.

The above-described embodiments are merely examples, and should not be construed as limiting the scope of the present invention. The scope of the present invention is defined by the scope of claims, and all variations and modifications within the equivalent scope of the claims are within the scope of the invention.

The present invention provides an engine body having a cylinder forming a combustion chamber, a piston inserted into the cylinder, and an intake valve and an exhaust valve arranged above the cylinder and opening and closing an intake port and an exhaust port, respectively; It is useful for a supercharged two-stroke engine provided with a supercharger provided in an intake passage connected to an intake port of an engine body.

1 2-stroke engine with supercharger 10 engine body 11 cylinder 15 piston 16 combustion chamber 19 intake port 20 exhaust port 21 intake valve 22 exhaust valve 30 electric intake S-VT (intake variable valve mechanism)
40 exhaust electric S-VT (exhaust variable valve mechanism)
50 intake passage 53 mechanical supercharger 100 ECU (control means) (ignitability estimating means) (compression end temperature estimating means)
SN4 intake air temperature sensor (outside temperature detection means)
SN5 engine water temperature sensor (engine water temperature detection means)
SN6 oil temperature sensor (oil temperature detection means)
SN7 linear _O2 sensor (ignitability estimation means)

Claims (4)

An engine body having a cylinder forming a combustion chamber, a piston inserted into the cylinder, an intake valve and an exhaust valve arranged above the cylinder and opening and closing an intake port and an exhaust port, respectively; an intake of the engine body A supercharged two-stroke engine comprising a supercharger provided in an intake passage connected to a port,
a variable valve mechanism capable of changing valve opening timing and valve closing timing of the intake valve and the exhaust valve;
ignitability estimation means for estimating the ignitability of the fuel supplied into the combustion chamber;
further comprising control means for controlling the operation of the variable valve mechanism,
The valve opening period of the intake valve and the exhaust valve includes a compression bottom dead center, the opening timing of the intake valve is later than the opening timing of the exhaust valve, and the closing timing of the intake valve is the exhaust valve. is set to satisfy a specific condition that it is substantially the same as the closing timing of the exhaust valve or later than the closing timing of the exhaust valve,
The variable valve mechanism is a valve mechanism that interlocks and changes both the valve opening timing and the valve closing timing while keeping the valve opening periods of the intake valve and the exhaust valve constant,
The control means is configured to perform compression self-ignition combustion of the fuel in a low-load operating region in which the engine load of the engine body is lower than a predetermined load,
The supercharger is configured to operate when the operating state of the engine body is in a compression self-ignition combustion region in which the fuel is subjected to compression self-ignition combustion,
Further, when the operating state of the engine body is in the compression ignition combustion region, the control means adjusts the opening timing of the intake valve and the exhaust valve as the ignitability estimated by the ignitability estimation means decreases. And the valve closing timing is advanced so that the effective compression ratio of the engine body is higher and the scavenging pressure in the scavenging stroke is lower than when the ignitability is high while the specific conditions are satisfied, A two-stroke engine with a supercharger, characterized in that it is configured to operate the variable valve mechanism. In the supercharged two-stroke engine according to claim 1,
The fuel includes gasoline,
The ignitability estimating means is configured to estimate the mixing ratio of ethanol to the gasoline, and to estimate that the higher the estimated mixing ratio of ethanol is, the lower the ignitability of the fuel. 2-stroke engine with supercharger. In the supercharged two-stroke engine according to claim 1,
The fuel includes light oil,
The ignitability estimation means is configured to estimate the cetane number of the light oil, and estimate that the lower the estimated cetane number, the lower the ignitability of the fuel. 2 stroke engine. In the supercharged two-stroke engine according to any one of claims 1 to 3,
outside temperature detection means for detecting outside temperature;
engine water temperature detection means for detecting the temperature of engine cooling water in the engine body;
oil temperature detection means for detecting the temperature of engine oil in the engine body;
When the operating state of the engine body is in the compression self-ignition combustion region, depending on the detection results of the outside air temperature detection means, the engine water temperature detection means, and the oil temperature detection means, and the ignitability of the fuel is the gas temperature in the combustion chamber at compression top dead center based on the effective compression ratio of the engine body when it is assumed that the closing timings of the intake valve and the exhaust valve are changed by the variable valve mechanism. Compression end temperature estimating means for estimating compression end temperature,
When the operating state of the engine body is in the compression self-ignition combustion region, the control means controls the ignitability estimated by the ignitability estimating means as well as the compression end temperature estimated by the compression end temperature estimating means. It is configured to operate the variable valve mechanism in consideration of temperature,
Further, when the compression end temperature estimated by the compression end temperature estimating means exceeds a predetermined temperature range, which is a temperature range in which self-ignition and combustion of fuel are possible, the control means sets the above-mentioned while correcting the valve opening timing and valve closing timing of the intake valve and the exhaust valve to the retard side from the set valve opening timing and valve closing timing within the range that satisfies the specific condition, the compression end temperature estimating means When the compression end temperature estimated by is below the predetermined temperature range, the valve opening timing and the valve closing timing of the intake valve and the exhaust valve set based on the ignitability are changed to a range that satisfies the specific condition , A two-stroke engine with a supercharger , wherein the set valve opening timing and valve closing timing are corrected to the advance side.

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