JP2020045837A - Two-stroke engine with supercharger - Google Patents

Abstract

To provide a two-stroke engine which performs compression ignition combustion, for suppressing the worsening of thermal efficiency and the worsening of emission performance while actualizing high combustion stability and appropriate engine torque.SOLUTION: An engine body 10 performs compression ignition combustion at least during low loading when an engine load is lower than a predetermined load. An intake valve 21 and an exhaust valve 22 are constructed so that a valve opening timing for the intake valve 21 is later than a valve opening timing for the exhaust valve 22, a valve closing timing for the intake valve 21 is almost the same as a valve closing timing for the exhaust valve 22 or later than the valve closing timing for the exhaust valve 22, and a valve opening period for each of them holds a compression bottom dead center therebetween. During the operation of a mechanical supercharger 53, when an estimated compression end temperature is higher than a target temperature, an ECU 100 allows the operation of an intake electric actuator S-VT30 to make the valve closing timing for the intake valve 21 later so that the effective compression ratio is lower.SELECTED DRAWING: Figure 8

Description

  The technology disclosed herein belongs to the technical field related to a supercharged two-stroke engine.

  Conventionally, a two-stroke engine in which a supercharger is provided in an intake passage is known (for example, Patent Document 1).

  For example, in Patent Document 1, scavenging in a cylinder is performed by opening both an intake valve that opens and closes an intake passage and an exhaust valve that opens and closes an exhaust passage during a scavenging period near the piston bottom dead center. There is disclosed a two-stroke engine having a fixed valve lift characteristic and having a supercharger in the intake passage, which is driven by rotation of a crankshaft and is constituted by a roots blower.

  Further, in Patent Document 1, a two-stroke engine is provided with a variable valve operating device for variably controlling the opening / closing timing of an intake valve, and when the engine load is a partial load (low load), the intake valve is closed. It is disclosed that the valve timing is delayed to provide a period in which gas in the combustion chamber is blown back to the intake port.

JP 2009-036144 A

  By the way, when the compression ignition combustion is performed when the engine load is lower than the predetermined load, it is necessary to increase the compression end temperature in the combustion chamber to some extent. If the valve closing time of the intake valve is simply delayed at a low load as in Patent Document 1, an appropriate compression end temperature may not be obtained, and combustion stability may be reduced. Also, if the gas in the combustion chamber is blown back to the intake port, the engine torque will decrease.

  On the other hand, if the compression end temperature becomes too high, there is a possibility that premature ignition may cause a decrease in engine thermal efficiency and an increase in combustion noise. On the other hand, if the compression end temperature is too high, the combustion temperature becomes high, NOx is easily generated, and the emission performance deteriorates.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to obtain high combustion stability and appropriate engine torque in a two-stroke engine that performs compression ignition combustion. Another object of the present invention is to suppress deterioration of thermal efficiency and emission performance.

  In order to solve the above-mentioned problem, in the technology disclosed herein, a cylinder forming a combustion chamber, a piston fitted into the cylinder, and an intake valve that opens and closes an intake port disposed above the cylinder are provided. A two-stroke engine with a supercharger, comprising: an engine body having an exhaust valve for opening and closing an exhaust port disposed above the cylinder, wherein a supercharger is provided in an intake passage connected to the engine body. An intake valve operating mechanism for changing the valve closing timing of the intake valve; a compression end temperature estimating means for estimating a gas temperature in the combustion chamber at a compression top dead center; and a control for controlling an operation of the intake valve operating mechanism. Means, wherein the engine body performs compression ignition combustion at least when the engine load is lower than a predetermined load, and the intake valve and the exhaust valve are the same as those of the intake valve. The valve timing is later than the opening timing of the exhaust valve, and the closing timing of the intake valve is substantially the same as the closing timing of the exhaust valve, or later than the closing timing of the exhaust valve, and each opening period. Is configured to sandwich the bottom dead center, and the control means, when the supercharger is operating, the estimated compression end temperature estimated by the compression end temperature estimating means is set to be smaller than a preset target temperature. When the intake valve timing is too high, the intake valve operating mechanism is operated to retard the valve closing timing of the intake valve so that the effective compression ratio becomes low.

  According to this configuration, when the closing timing of the intake valve is delayed, the position of the piston at the start of compression becomes closer to the compression top dead center, and the effective compression ratio decreases. On the other hand, by supplying the supercharged intake air to the combustion chamber, the intake air in the combustion chamber blows to the intake port even when the intake valve is open when the piston is operating toward the compression top dead center. It will not be returned. Therefore, by delaying the closing timing of the intake valve, it is possible to lower the effective compression ratio while keeping the intake air amount constant. As a result, the compression end temperature can be reduced to the target temperature, so that deterioration of thermal efficiency due to premature ignition can be suppressed, and deterioration of emission performance can be suppressed. Further, since the amount of intake air supplied to the combustion chamber becomes constant, high combustion stability and appropriate engine torque can be obtained. As a result, in a two-stroke engine that performs compression ignition combustion, it is possible to suppress deterioration in thermal efficiency and emission performance while obtaining high combustion stability and appropriate engine torque.

  In one embodiment of the supercharger-equipped two-stroke engine, the turbocharger further includes an exhaust valve operating mechanism for changing a valve closing timing of the exhaust valve, and the control means further controls the operation of the exhaust valve operating mechanism. When the estimated compression end temperature is lower than the target temperature during the operation of the supercharger, the control means advances the closing timing of the intake valve so that the effective compression ratio increases. In order to operate the intake valve operating mechanism so as to be angular, to maintain a condition that the closing timing of the exhaust valve is substantially the same as the closing timing of the intake valve or earlier than the closing timing of the intake valve. It is configured to operate the exhaust valve mechanism.

  According to this configuration, when the closing timing of the intake valve and the exhaust valve is advanced, the position of the piston at the start of compression becomes a position farther from the compression top dead center, and the effective compression ratio increases. As a result, the compression end temperature can be set to the target temperature, and high combustion stability can be obtained.

  In the two-stroke engine with a supercharger, the compression end temperature estimating means is configured to estimate the compression end temperature in consideration of the engine load, and the control means sets the intake valve as the engine load increases. May be configured to operate the intake valve operating mechanism in order to delay the valve closing timing.

  That is, the higher the engine load, the greater the fuel supply amount and the higher the combustion pressure and combustion temperature, so that the compression end temperature tends to increase. For this reason, it is possible to suppress an abnormal increase in the combustion pressure and the combustion temperature by delaying the closing timing of the intake valve as the engine load increases. As a result, deterioration of thermal efficiency can be more effectively suppressed, and deterioration of emission performance can be suppressed more effectively.

  In 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 an engine cooling water of the engine body, and a temperature of an engine oil of the engine body. An oil temperature detecting means, wherein the compression end temperature estimating means calculates a detection result of each of the outside air temperature detecting means, the engine water temperature detecting means and the oil temperature detecting means, and an effective compression ratio of the engine body. The configuration may be such that the compression end temperature is estimated in consideration of this.

  According to this configuration, the accuracy of estimating the compression end temperature can be improved by taking into account the temperature of the engine cooling water, the temperature of the engine oil, and the effective compression ratio of the engine body, which correspond to the temperature of the engine body. As a result, the control based on the estimated compression end temperature can be appropriately executed, and as a result, high combustion stability and appropriate engine torque can be more appropriately obtained, and the deterioration of thermal efficiency and the deterioration of emission performance are more effectively achieved. Can be suppressed.

  In the two-stroke engine with a supercharger, the intake valve operating mechanism is configured to change both the opening timing and the closing timing of the intake valve in an interlocking manner while keeping the opening period of the intake valve constant. It may be a type of a valve operating mechanism.

  According to this configuration, the configuration of the intake valve operating mechanism can be a simple configuration that does not require changing the valve opening period and the lift amount of the intake valve.

  As described above, according to the technology disclosed herein, by delaying the closing timing of the intake valve, the effective compression ratio can be increased while the intake amount of the gas in the combustion chamber at the start of compression is kept constant. Can be lower. As a result, deterioration of thermal efficiency due to premature ignition can be suppressed, and deterioration of emission performance can be suppressed. Further, since the amount of intake air supplied to the combustion chamber becomes constant, high combustion stability and appropriate engine torque can be obtained. As a result, in a two-stroke engine that performs compression ignition combustion, it is possible to suppress deterioration in thermal efficiency and emission performance while obtaining high combustion stability and appropriate engine torque.

1 is a schematic configuration diagram of a two-stroke engine with a supercharger according to an embodiment. It is a schematic diagram showing connection relation between a mechanical type supercharger and a two-stroke engine with a supercharger. FIG. 2 is a block diagram illustrating a control system of a two-stroke engine with a supercharger. 4 is a performance curve graph showing characteristics of a compressor of a mechanical supercharger. It is a figure showing an example of an opening and closing pattern of an intake valve and an exhaust valve. FIG. 4 is a diagram illustrating a state in the cylinder during a scavenging stroke, in which only an exhaust valve is opened. FIG. 4 is a diagram showing a state in the cylinder during a scavenging stroke, showing a state in which both an intake valve and an exhaust valve are open. 5 is a graph showing a change in compression end temperature when an intake valve and an exhaust valve are retarded or advanced. 5 is a graph showing a change in engine torque when an intake valve and an exhaust valve are retarded or advanced. FIG. 3 is a diagram illustrating a state in a cylinder when only an intake valve is open. FIG. 3 is a diagram illustrating a state in a cylinder when the closing timing of an intake valve and an exhaust valve is advanced. It is a figure which shows an example of the opening / closing pattern of an intake valve and an exhaust valve when an estimated compression end temperature is higher than a target temperature. It is a figure which shows an example of the opening / closing pattern of an intake valve and an exhaust valve when an estimated compression end temperature is lower than a target temperature. 5 is a flowchart illustrating a processing operation of the ECU.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

  FIG. 1 shows a two-stroke engine 1 with a supercharger according to the present embodiment (hereinafter abbreviated as engine 1). The engine 1 is an engine mounted on a vehicle. The engine body 10 of the engine 1 is a gasoline engine to which fuel mainly containing gasoline is supplied, and includes a cylinder block 12 provided with a plurality of cylinders 11 (only one is shown in FIG. 1). And a cylinder head 13 disposed on the cylinder block 12. The plurality of cylinders 11 are arranged so 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 inserted into each cylinder 11 of the engine body 10 so as to be reciprocally slidable. A combustion chamber 16 is defined by the piston 15, the cylinder block 12, and the cylinder head 13. . The combustion chamber 16 is a so-called pent roof type combustion chamber 16, and the wall surface of the cylinder head 13 that forms the combustion chamber 16 has two inclined surfaces 13 a and 13 b. The piston 15 is connected to a crankshaft 18 via a connecting rod 17 in the cylinder block 12. 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 operating mechanism, and an intake port 19 and an exhaust port 20 communicating with the combustion chamber 16 are formed in the cylinder head 13 for each cylinder 11. That is, the intake port 19 and the exhaust port 20 are arranged above the 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 combustion chamber 16 side. Each exhaust port 20 is provided with an exhaust valve 22 that opens and closes an opening of each exhaust port 20 on the combustion chamber 16 side. The opening of each intake port 19 on the combustion chamber 16 side is formed on one of the two inclined surfaces 13a and 13b of the cylinder head 13 (hereinafter, referred to as an intake-side inclined surface 13a). The opening on the 16 side is formed on the other of the two inclined surfaces 13a and 13b of the cylinder head 13 (hereinafter, referred to as an exhaust-side inclined surface 13b).

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

  On the other hand, the exhaust port 20 is connected to an exhaust passage 60 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. I have.

  An intake camshaft 31 for operating each intake valve 21 and an exhaust camshaft 41 for operating each exhaust valve 20 are provided in the cylinder head 13. Each camshaft 31, 41 is connected to the crankshaft 18 via a power transmission mechanism such as a chain / sprocket mechanism (not shown). Thereby, each of the camshafts 31 and 41 rotates in conjunction with the rotation of the crankshaft 18.

  The intake camshaft 31 is provided with a variable valve mechanism for varying the valve timing. In the present embodiment, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 30. The intake electric S-VT 30 is configured to continuously change the rotation phase of the intake camshaft 31 within a predetermined angle range. That is, the intake electric S-VT 30 is a phase-type variable valve mechanism, and changes both the valve opening timing and the valve closing timing in conjunction with a fixed valve opening period. By the intake electric S-VT 30, the valve opening timing and the valve closing timing of the intake valve 21 change continuously. Note that the intake valve operating mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The exhaust camshaft 41 is also provided with a variable valve mechanism for varying the valve timing. In the present embodiment, this variable valve mechanism has an exhaust electric S-VT40. The exhaust electric S-VT 40 is configured to continuously change the rotation phase of the exhaust camshaft 41 within a predetermined angle range. That is, the exhaust electric S-VT 40 is a phase type variable valve mechanism, and changes both the valve opening timing and the valve closing timing in an interlocked manner while keeping the valve opening period constant. With the exhaust electric S-VT 40, the valve opening timing and the valve closing timing of the exhaust valve 22 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  In the present embodiment, the intake electric S-VT 30 and the exhaust electric S-VT 40 both change the valve timing within a predetermined angle range, but change the valve lift within a predetermined angle range. You may.

  As shown in FIG. 1, the cylinder head 13 is provided with a fuel injection valve 23 for injecting fuel into the combustion chamber 16 for each cylinder 11. The fuel injection valve 23 is disposed such that its injection port faces the inside of the combustion chamber 16 from the ceiling of the combustion chamber 16. The fuel injection valve 23 directly injects an amount of fuel into the combustion chamber 16 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1.

  An ignition plug 24 for burning fuel injected into the cylinder 11 is attached to the cylinder head 13 for each cylinder 11. As shown in FIG. 1, the spark plug 24 is arranged such that the electrode 24 a faces the combustion chamber 16 from the one side (that is, the exhaust side) of the cylinder head 13 in the engine width direction. The ignition plug 24 receives a control signal from the ECU 100 described later and energizes the electrode 24a so as to generate a spark at a desired ignition timing.

  As shown in FIG. 1, an intake passage 50 is connected to the other surface of the engine body 10 in the engine width direction so as to communicate with the intake port 19 of each cylinder 11. On the other hand, the one surface in the engine width direction of the engine body 10 is connected to communicate with the exhaust port 20 of each cylinder 11 and discharges 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 an upstream end of the intake passage 50. On the other hand, a surge tank 52 is provided near the downstream end of the intake passage 50. An intake passage 50 downstream of the surge tank 52 is an independent intake passage branched for each cylinder 11, and the downstream ends of the independent intake passages are connected to the intake ports 19 of each cylinder 11, respectively.

  A mechanical supercharger 53 is disposed 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 upstream of the mechanical supercharger 53 is referred to as an upstream intake passage 50a, and a portion of the intake passage 50 downstream of the mechanical supercharger 53 is downstream. It is called a side intake passage 50b.

  The mechanical supercharger 53 is a supercharger that does not use exhaust energy, and more specifically, is a turbocharger that is driven to rotate 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. Have been. Specifically, a first pulley 71 is attached to the crankshaft 18, and a second pulley 72 is attached to an input shaft 53 b of a compressor 53 a of the mechanical supercharger 53. In FIG. 2, the surge tank 52 and the exhaust passage 60 are omitted.

  Since the mechanical supercharger 53 is driven to rotate by the rotation of the crankshaft 18, the rotation speed is proportional to the rotation speed of the crankshaft 18 (that is, the engine rotation speed). The diameter of each of the first and second pulleys 71 and 72 is set such that the rotation speed of the compressor 53a becomes a desired rotation speed. Note that 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.

  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 an outer end of the exhaust port 20 and a collective portion where the independent exhaust passages gather. ing.

An exhaust purification catalyst 61 is disposed downstream of the exhaust manifold in the exhaust passage 60. The exhaust purification catalyst 61 is an oxidation catalyst, and promotes a reaction in which CO and HC in the exhaust gas are oxidized to generate CO ₂ and H ₂ O. Although not shown in the drawings, a portion of the exhaust passage 60 downstream of the exhaust purification catalyst 61 collects fine particles such as soot contained in the exhaust gas of the engine 1. A filter is provided. This engine 1 is not provided with a catalyst for purifying NOx. However, the present disclosure does not exclude application to an engine having a catalyst for purifying NOx.

  As shown in FIG. 3, the engine 1 is controlled by an ECU (Engine Control Unit) 100. The ECU 100 is a controller based on a known microcomputer. 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 a computer program (including a basic control program such as an OS and an application program activated on the OS to realize a specific function). The memory 102 includes a RAM and a ROM. The ROM stores various computer programs (particularly, control programs for controlling the engine 1), data including a map described later used when executing the computer programs, and the like. 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 electric signals to and from the ECU 100.

  The ECU 100 includes a crank angle sensor SN1, an air flow sensor SN2, an accelerator opening sensor SN3, an intake air temperature sensor SN4 (outside air temperature detecting means), an engine water temperature sensor SN5 (engine water temperature detecting means), and an oil temperature sensor SN6 (oil temperature detecting means). ) Are electrically connected. The crank angle sensor SN1 is provided in the cylinder block 12, and detects the rotation angle of the crank shaft 18. The airflow sensor SN2 detects the flow rate of intake air in the upstream intake passage 50a. The accelerator opening sensor SN3 is attached to the accelerator pedal mechanism of the vehicle, and detects an accelerator opening corresponding to the operation amount of the accelerator pedal. The intake air temperature sensor SN4 detects the temperature of intake air in the upstream intake passage 50a. The engine water temperature sensor SN5 detects the temperature of engine cooling water flowing through the water jacket 12a. The oil temperature sensor NS6 detects the temperature of the engine oil. These sensors SN1 to SN6 and the like output detection signals to the ECU 100.

  The ECU 100 calculates the engine speed from the detection result of the crank angle sensor SN1. The ECU 100 calculates the engine load from the detection result of the accelerator opening sensor SN3.

  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 water temperature sensor SN5, the detection result of the oil temperature sensor SN6, the effective compression ratio of the engine body 10, and the detection of the accelerator opening sensor SN3. Based on the engine load calculated from the result, a compression end temperature that is a gas temperature in the combustion chamber 16 at the compression top dead center is estimated. From this, the ECU 100 corresponds to a compression end temperature estimating means for estimating the gas temperature in the combustion chamber 16 at the compression top dead center.

  The ECU 100 determines the operating state of the engine 1 based on the input signals from the sensors SN1 to SN6 and the like, and controls the engine such as the fuel injection valve 23, the spark plug 24, the intake electric S-VT30, and the exhaust electric S-VT40. A control signal is output to each device to control each device.

  FIG. 4 shows the performance characteristics of the compressor 53a of the mechanical supercharger 53. The vertical axis represents the ratio of the pressure in the downstream intake passage 50b to the pressure in the upstream intake passage 50a (hereinafter simply referred to as the pressure ratio), and the horizontal axis represents the discharge flow rate from the compressor 53a. In FIG. 4, a curve RL represents a rotation limit line, and a substantially straight line SL 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 area. In the present embodiment, since the pressure in the upstream intake passage 50a is basically atmospheric pressure, the level of the pressure ratio indicates the level of the supercharging pressure by the mechanical supercharger 53. I have.

  The plurality of curves RSL illustrated in the operable region are lines connecting operating points at which the number of rotations of the compressor 53a is equal, and the number of rotations is higher as the rotation point is closer to the rotation limit line RL. A dashed-dotted line BL extending so as to vertically extend the operable region of the mechanical supercharger 53 is a line connecting operating points at which the operating efficiency of the compressor 53a is the best for each rotation speed of the compressor 53a. .

  Since the compressor 53a is constituted by a centrifugal blower, the compressor 53a basically shows a tendency that the higher the rotation 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 supercharging pressure. When the engine speed is low, the actual time during which the intake valve 21 and the exhaust valve 22 open per cycle of the engine 1 is long, so that the exhaust gas can be scavenged even when the supercharging pressure is low. On the other hand, when the engine speed is high, the actual time during which the intake valve 21 and the exhaust valve 22 open per cycle of the engine 1 is short, so that the intake air is introduced into the combustion chamber 16 at the highest possible boost pressure. Therefore, it is necessary to scavenge the exhaust gas at an early stage. Therefore, the compressor 53a has the above-described characteristics, so that appropriate exhaust gas scavenging can be performed.

  The supercharging pressure and the flow rate of the intake air to be supplied to the combustion chamber 16 in order to efficiently scavenge the exhaust gas can be obtained in advance based on the engine specifications of the engine body 10 (such as the volume of the combustion chamber 16). For this reason, in the present embodiment, the required supercharging pressure and intake air flow rate are calculated based on the engine specifications of the engine body 10, and the mechanical supercharger in which the operating point is located on the broken line BL 53 has been selected. Thereby, supercharging can be efficiently performed in accordance with the engine speed.

  FIG. 5 shows the lift characteristics of the intake valve 21 and the exhaust valve 22 during normal running of the vehicle. The abscissa represents the crank angle. The crank angle at the compression top dead center is defined as 0 °. Later) is indicated by a plus. In FIG. 5, −360 ° corresponds to the compression top dead center in the combustion cycle one cycle before.

  As shown in FIG. 5, in the present embodiment, the intake valve 21 and the exhaust valve 22 are such that the opening timing of the intake valve 21 is about 20 ° later than the opening timing of the exhaust valve 22 during normal running of the vehicle, and The closing timing of the intake valve 21 is configured to be substantially the same as the closing timing of the exhaust valve 22. Further, the intake valve 21 and the exhaust valve 22 are configured so that their respective valve opening periods sandwich a bottom dead center (BDC). More specifically, the intake valve 21 and the exhaust valve 22 exhibit the above-described lift characteristics by the intake and exhaust camshafts 31 and 41 and the intake and exhaust valve mechanisms 30 and 40. Note that “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 shorter than the closing timing of the exhaust valve 22 (2 ° in crank angle). (Approximately 3 °)) and both when the closing timing of the intake valve 21 is slightly later than the closing timing of the exhaust valve 22. In the present embodiment, the closing timing of the intake valve 21 is slightly later than the closing timing of the exhaust valve 22.

  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 flushing to port 20. When entering the scavenging stroke in the combustion cycle, the exhaust valve 22 opens earlier than the intake valve 21 as described above. This is to prevent the exhaust gas from flowing into the intake port 21.

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

  As shown in FIG. 6, after the fuel is burned in the combustion cycle one cycle before, first, only the exhaust valve 22 is 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 by the combustion pressure.

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

  As shown in FIGS. 5 and 7, when the piston 15 is rising toward the compression top dead center, the exhaust valve 22 is also opened. Thereby, the exhaust gas in the combustion chamber 16 is pushed to the exhaust port 20 by the intake air supplied to the combustion chamber 16 and the rise of the piston 15.

  Next, as shown in FIG. 5, the intake valve 21 and the exhaust valve 22 are closed at substantially the same timing. Specifically, in the present embodiment, the intake valve 21 is closed slightly after the exhaust valve 22 is closed. Thereafter, the intake air in the combustion chamber 16 (the intake air and the residual gas when a part of the exhaust gas remains in the combustion chamber 16) is compressed by the rise of the piston 15.

  Thereafter, fuel is injected into the combustion chamber 16 by the fuel injection valve 23. Then, at least when the engine load is lower than the predetermined load, the fuel is burned by compression ignition. On the other hand, when the engine load is higher than the predetermined load, the fuel may be burned by compression ignition as in the case of low engine load, or the fuel may be forcibly burned by spark ignition by the spark plug 24. You may. The term "compression ignition" includes combustion in which fuel is combusted by compression ignition after assisting ignition by the ignition plug 24 (SPCCI combustion).

  Here, as described above, when fuel is combusted by compression ignition, it is necessary to appropriately secure the compression end temperature of the combustion chamber 16 in order to stabilize combustion. On the other hand, if the compression end temperature becomes too high, there is a possibility that premature ignition may cause a decrease in engine thermal efficiency and an increase in combustion noise. On the other hand, if the compression end temperature is too high, NOx is likely to be generated, and the emission performance deteriorates.

  Therefore, in the present embodiment, the ECU 100 estimates the compression end temperature and sets the intake valve 21 and the exhaust valve so that the compression end temperature becomes a target temperature at which fuel can be stably burned by compression ignition. The valve closing timing of the valve 22 is adjusted. The target temperature is, for example, about 1000K and has a range of about ± 20K. In the present embodiment, the closing timing of the intake valve 21 and the exhaust valve 22 is defined at the time of a 1 mm lift.

  FIG. 8 shows a result of calculating, by simulation, a change in the compression end temperature when the closing timing of the intake valve 21 and the exhaust valve 22 is adjusted. FIG. 9 shows a result of calculating, by simulation, a change in engine torque when the closing timing of the intake valve 21 and the exhaust valve 22 is adjusted. In the simulations of FIGS. 8 and 9, the engine speed is set to 1500 rpm and the air-fuel ratio is set to A / F = 30.

  8, the vertical axis indicates the compression end temperature, and the horizontal axis indicates the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22. The horizontal axis represents the valve closing timing in the case of the opening and closing pattern shown in FIG. In the present embodiment, both the intake electric S-VT 30 and the exhaust electric S-VT 40 are of the phase type, so that when the valve closing timing changes, the valve opening timing also changes in conjunction therewith. In the graph shown in FIG. 8, a diamond indicates a case where the intake valve 21 and the exhaust valve 22 are synchronized and the valve closing timing is retarded or advanced by the same amount, and a triangle indicates that only the intake valve 21 is retarded or advanced. The square indicates a case where only the exhaust valve 22 is retarded or advanced. The dotted line shown in FIG. 8 represents an example of the target temperature. In this simulation, it is assumed that the opening timing of the intake valve 21 is not earlier than the opening timing of the exhaust valve 22. For this reason, the advance amount when only the intake valve 21 advances the valve closing timing is up to 20 °, and the retard amount when only the exhaust valve 22 retards the valve closing timing is also up to 20 °. It has become. 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. 9, the vertical axis represents the engine torque, and the horizontal axis represents the amount of change in the closing timing of the intake valve 21 and the exhaust valve 22. The notation on the horizontal axis and the marks indicating the targets of the advance and retard are the same as those in FIG.

  As shown in FIG. 8, when the valve closing timing is retarded by synchronizing the intake valve 21 and the exhaust valve 22, the compression end temperature decreases as the retard amount increases. Also, when the valve closing timing of only the intake valve 21 is retarded, 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. This is because the delay of the closing timing of the intake valve 21 causes the position of the piston 15 at the start of compression to be close to the compression top dead center, and the effective compression ratio changes.

  On the other hand, when the valve closing timing of only the exhaust valve 21 is retarded, it can be seen that the compression end temperature only slightly decreases. As described above, in this simulation, when the valve closing timing changes, the valve opening timing also changes in conjunction therewith. When the valve opening timing of the exhaust valve 22 is delayed, the exhaust valve 22 is opened when the in-cylinder pressure is low, so that exhaust gas is not easily discharged. As a result, the amount of exhaust gas remaining in the combustion chamber 16 at the start of compression increases. As a result, even if only the exhaust valve 22 delays the valve closing timing to lower the effective compression ratio, the compression end temperature is less likely to decrease.

  Here, when the valve closing timing of only the intake valve 21 is retarded, as shown in FIG. 10, when the piston 15 is at a position close to the compression top dead center, only the intake valve 21 is opened. However, in the present 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 far from the exhaust port 20. The flow 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 the intake air supercharged by the mechanical supercharger 53. As a result, in this embodiment, as shown in FIG. 10, even if only the intake valve 21 is opened when the piston 15 is raised, the supercharged intake air is supplied to the combustion chamber 16. Therefore, there is almost no blowback from the combustion chamber 16 to the intake port 19.

  If there is almost no blowback from the combustion chamber 16 to the intake port 19, the amount of intake air supplied to the combustion chamber 16 is constant. Specifically, when the engine speed is constant and the rotational 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 blow-back from the combustion chamber 16 to the intake port 19, the amount of intake air supplied to the combustion chamber 16 is constant. For this reason, as shown in FIG. 9, the engine torque hardly changes even when the valve closing timing of the intake valve 21 is retarded.

  On the other hand, referring to FIG. 8, when the intake valve 21 and the exhaust valve 22 are synchronized to advance each valve closing timing, it is understood that the compression end temperature increases as the advance amount increases. This is because the amount of exhaust gas in the combustion chamber 16 increases in addition to the increase in the effective compression ratio. That is, as shown in FIG. 11, when the valve closing timing is advanced by synchronizing the intake valve 21 and the exhaust valve 22, the position of the piston 15 moves from a position farther from the compression top dead center to the combustion chamber 16 Since the compression of the gas inside is started, the effective compression ratio decreases. Further, when the valve closing timing of the intake valve 21 is advanced, the intake air is introduced into the combustion chamber 16 at a position where the piston 15 is close to the bottom dead center. The scavenging pressure at the time of scavenging the exhaust gas decreases. This suppresses the scavenging of exhaust gas, so that the amount of exhaust gas in the combustion chamber 16 at the start of compression increases as shown in FIG.

  Referring to FIG. 8, when the valve closing timing of only the intake valve 21 is advanced, the compression end temperature rises. However, when compared with the case where the intake valve 21 and the exhaust valve 22 are synchronized, the compression end temperature increases. Is small. If the closing timing of only the intake valve 21 is advanced, the closing timing of the exhaust valve 22 is later than the closing timing of the intake valve 21, so that the effective compression ratio is determined by the closing timing of the exhaust valve 22. Therefore, 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 decreases, and the amount of exhaust gas in the combustion chamber 16 at the start of compression increases. For this reason, the compression end temperature rises even if the closing timing of only the intake valve 21 is advanced, but the amount of increase in the compression end temperature is smaller than when the intake valve 21 and the exhaust valve 22 are synchronized. . Also, it can be seen that when the advance amount is 20 °, it is almost the same as when the advance amount is 10 °. This is because the effective compression ratio is determined by the closing timing of the exhaust valve 22, and the effective compression ratio does not change even if the closing timing of the intake valve 21 is advanced.

  Referring to FIG. 8, it can be seen that when the valve closing timing of only the exhaust valve 22 is advanced, the compression end temperature hardly changes. This is because the valve closing timing of the intake valve 21 does not change and the effective compression ratio does not change even if the valve closing timing of only the exhaust valve 22 is advanced.

  Here, as described above, if the engine speed is constant and the discharge flow rate from the mechanical supercharger 53 is constant, even if the valve closing timing of the intake valve 21 is advanced, the combustion chamber 16 The supplied intake air amount becomes constant. For this reason, as shown in FIG. 9, the engine torque hardly changes even when the valve closing timing of the intake valve 21 is advanced.

  As described above, in the engine 1 of the present embodiment, by adjusting the closing timing of the intake valve 21 and the exhaust valve 22, the compression end temperature can be changed while securing the engine torque. At this time, as shown in FIG. 8, when the compression end temperature is lowered, the valve closing timing of the intake valve 21 may be simply retarded, but when the compression end temperature is raised, the intake valve 21 and the exhaust valve 22 may be closed. It is desirable to advance both. In particular, when the closing timing of only the intake valve 21 is advanced and the closing timing of the exhaust valve 22 is later than the closing timing of the intake valve 21, the intake air supplied to the combustion chamber 16 flows out to the exhaust port 20. For this reason, it is desirable that the closing timing of the exhaust valve 22 be substantially the same as the closing timing of the intake valve 21 or earlier than the closing timing of the intake valve 21.

  For this reason, in this embodiment, when the estimated compression end temperature is higher than the target temperature at least when the engine load is low and the engine load is lower than the predetermined load, as shown in FIG. The intake electric S-VT 30 is operated to retard the valve closing timing so that the effective compression ratio becomes low. On the other hand, when the estimated compression end temperature is lower than the target temperature, as shown in FIG. 13, the ECU 100 adjusts the valve timing of the intake valve 21 so as to advance the valve closing timing of the intake valve 21 so as to increase the effective compression ratio. While operating the VT 30, the exhaust electric S-VT 40 is operated to maintain the condition that the closing timing of the exhaust valve 22 is substantially the same as the closing timing of the intake valve 21.

  The ECU 100 increases the retard amount of the intake valve 21 as the estimated compression end temperature is higher than the target temperature, and increases the intake valve 21 and the exhaust valve 22 as the estimated compression end temperature is lower than the target temperature. To increase the lead angle. The relationship between the closing timing of the intake valve 21 and the exhaust valve 22 and the compression end temperature as shown in FIG. 8 is stored in the memory 102 of the ECU 100 as a map. Based on the difference between the estimated compression end temperature and the target temperature, the CPU 101 of the ECU 100 calculates the retard amount of the intake valve 21 so as to reach the estimated compression end temperature and the target temperature, or the advance angle of the intake valve 21 and the exhaust valve 22. The amount is calculated, and a control signal is sent to the intake electric S-VT 30 and the exhaust electric S-VT 40.

  Further, the ECU 100 activates the intake electric S-VT 30 to delay the closing timing of the intake valve 21 as the engine load calculated from the accelerator opening sensor SN3 increases. In other words, the higher the engine load, the greater the amount of fuel supplied, so the combustion pressure and combustion temperature are high, and the compression end temperature is likely to be high. For this reason, as the engine load is higher, the deterioration of the thermal efficiency of the engine and the increase of the combustion noise due to the premature ignition are more likely to occur, and the emission performance is more likely to be reduced. Therefore, the ECU 100 estimates that the compression end temperature increases as the engine load increases, and retards the closing timing of the intake valve 21 as the engine load increases. Thereby, it is possible to suppress the combustion pressure and the combustion temperature from becoming abnormally high. As a result, deterioration of thermal efficiency can be more effectively suppressed, and deterioration of emission performance can be suppressed more effectively. When the engine load is higher than the predetermined load, there is a concern that combustion noise may be generated due to a rapid increase in combustion pressure. Therefore, in order to suppress combustion noise, control for delaying the closing timing of the intake valve 21 is particularly effective.

  As described above, the ECU 100 sets the retard amount of the closing timing of the intake valve 21 and the advance amount of the closing timing of the intake valve 21 and the exhaust valve 22 while setting the respective valve opening periods. The retard amount and the advance amount are set within the range sandwiching the bottom dead center.

  Next, a processing operation of the ECU 100 when the intake valve 21 and the exhaust valve 22 are retarded or advanced based on the estimated compression end temperature will be described with reference to FIG. The processing operation based on this flowchart is executed every combustion cycle while the engine 1 is operating.

  In the first step S1, the ECU 100 reads signals from various sensors. At this time, the ECU 100 particularly determines the outside air temperature estimated from the detection result of the intake air temperature sensor SN4, the engine water temperature detected by the engine water temperature sensor SN5, the engine oil temperature detected by the oil temperature sensor SN6, and the current And the engine load calculated from the detection result of the accelerator opening sensor SN3. The current effective compression ratio is determined based on the current valve timing of the intake valve 21 and the exhaust valve 22.

  In the next step S2, the ECU 100 estimates the compression end temperature from the various parameters read in step S1.

  In the next step S3, the ECU 100 determines whether the estimated compression end temperature calculated in step S2 is outside the target temperature, that is, whether the estimated compression end temperature is higher or lower than the target temperature. Is determined. When the estimated compression end temperature is higher or lower than the target temperature (YES), the process proceeds to step S4. On the other hand, when the estimated compression end temperature is NO within the target temperature range, the process returns.

  In step S4, the ECU 100 determines whether or not the estimated compression end temperature is higher than the target temperature. When the estimated compression end temperature is higher than the target temperature (YES), the process proceeds to step S5. On the other hand, when the estimated compression end temperature is lower than the target temperature (NO), the process proceeds to step S7.

  In step S5, the ECU 100 calculates the retard amount of the closing timing of the intake valve 21. At this time, the ECU 100 calculates the amount of retard of the closing timing of the intake valve 21 based on the difference between the estimated compression end temperature and the target temperature. More specifically, the greater the difference between the estimated compression end temperature and the target temperature, the greater the amount of retard of the closing timing of the intake valve 21. After step S5, the process proceeds to step S6.

  In the next step S6, the ECU 100 operates the intake electric S-VT 30 to retard the closing timing of the intake valve 21. After step S6, the process returns.

  On the other hand, the process proceeds when the estimated compression end temperature is lower than the target temperature. In step S7, the ECU 100 calculates the advance amount of the closing timing of the intake valve 21 and the exhaust valve 22. At this time, the ECU 100 calculates the advance amount of the closing timing of the intake valve 21 and the exhaust valve 22 based on the difference between the estimated compression end temperature and the target temperature. More specifically, as the difference between the estimated compression end temperature and the target temperature increases, the advance amount of the closing timing of the intake valve 21 and the exhaust valve 22 increases. After step S7, the process proceeds to step S8.

  In the next step S8, the ECU 100 operates the intake electric S-VT 30 and the exhaust electric S-VT 40 to advance the closing timing of the intake valve 21 and the exhaust valve 22. After step S8, the process returns.

  Therefore, in the present embodiment, the intake valve 21 and the exhaust valve 22 have the opening timing of the intake valve 21 later than the opening timing of the exhaust valve 22 and the closing timing of the intake valve 21 is the closing timing of the exhaust valve 22. The ECU 100 is configured so that the estimated compression end temperature estimated by the ECU 100 during the operation of the mechanical supercharger 53 is determined in advance. When the temperature is higher than the set target temperature, the intake electric S-VT 30 is operated to retard the valve closing timing of the intake valve 21 so that the effective compression ratio becomes low. This makes it possible to lower the effective compression ratio and lower the compression end temperature to the target temperature, thereby suppressing deterioration in thermal efficiency and emission performance. On the other hand, since the amount of intake air supplied to the combustion chamber 16 can be constant, high combustion stability and appropriate engine torque can be obtained.

  When the estimated compression end temperature is lower than the target temperature, the ECU 100 activates the intake electric S-VT 30 so as to advance the valve closing timing of the intake valve 21 so as to increase the effective compression ratio. The exhaust electric S-VT 40 is operated to maintain the condition that the valve closing timing of the valve 22 is substantially the same as the valve closing timing of the intake valve 21. As a result, the effective compression ratio can be increased to raise the compression end temperature to the target temperature, and high combustion stability can be obtained.

  In particular, in the present embodiment, the retard amount of the closing timing of the intake valve 21 when the estimated compression end temperature is higher than the target temperature, and the intake valve 21 and the exhaust when the estimated compression end temperature is lower than the target temperature. The advance amount of the valve closing timing of the valve 22 is set based on the difference between the estimated compression end temperature and the target temperature. As a result, the compression end temperature can be appropriately set within the target temperature, and it is possible to suppress deterioration of thermal efficiency and emission performance while obtaining high combustion stability and appropriate engine torque.

  Further, in the present embodiment, the ECU 100 estimates the compression end temperature in consideration of the detection results of the intake air temperature sensor SN4, the engine water temperature sensor SN5, and the oil temperature sensor SN6, and the effective compression ratio of the engine body 10. According to this, the accuracy of estimating the compression end temperature is improved by taking into account the temperature of the engine coolant and the temperature of the engine oil corresponding to the temperature of the engine body 10 and the effective compression ratio of the engine body 10. Can be. As a result, the control based on the estimated compression end temperature can be appropriately executed, and as a result, high combustion stability and appropriate engine torque can be more appropriately obtained, and the deterioration of thermal efficiency and the deterioration of emission performance are more effectively achieved. Can be suppressed.

  The technology disclosed herein is not limited to the above embodiment, and may be substituted without departing from the scope of the claims.

  For example, in the above-described embodiment, the intake valve 21 and the exhaust valve 22 are configured such that the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22, but the invention is not limited thereto. The intake valve 21 and the exhaust valve 22 have a later closing timing of the intake valve 21 than a closing timing of the exhaust valve 22 (at least 4 ° later in crank angle) at a normal valve timing that does not delay the closing timing. It may be constituted so that it may become.

  Further, in the above-described embodiment, since both the intake valve operating mechanism and the exhaust valve operating mechanism are of the phase type, when the closing timing of the intake valve 21 is retarded, and when the intake valve 21 and the exhaust valve 22 are closed. When the valve timing is advanced, the respective valve opening timings are also retarded or advanced in synchronization with each other, but the invention is not limited thereto, and the intake valve operating mechanism and the exhaust valve operating mechanism are configured to be able to change the valve lift. In this case, only the valve closing timing may be retarded or advanced.

  Further, in the above-described embodiment, the ECU 100 calculates 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 detection result of the crank angle sensor SN1. The compression end temperature which is the gas temperature in the combustion chamber 16 at the compression top dead center is estimated based on the compression allowance and the engine load calculated from the detection result of the accelerator opening sensor SN3. The detection result of the water temperature sensor SN5 and the detection result of the oil temperature sensor SN6 may not be used. That is, the change in the engine water temperature or the engine oil temperature has a time lag with respect to the change in the temperature of the combustion chamber 16. This is because it is sometimes preferable not to refer to the temperature.

  Further, in the above-described embodiment, when the estimated compression end temperature is higher than the target temperature, the closing timing of only the intake valve 21 is retarded. However, the present invention is not limited to this. You may make it retard. At this time, the ECU 100 determines that the opening timing of the intake valve 21 is later than the opening timing of the exhaust valve 22 and that the closing timing of the intake valve 21 is substantially the same as the closing timing of the exhaust valve 22 or that the exhaust valve 22 is closed. The retard angles of the intake valve 21 and the exhaust valve 22 are set so as to satisfy the condition that the valve opening period is later than the valve timing and the respective valve opening periods sandwich the bottom dead center. Further, as long as the above condition is satisfied, the ECU 100 may make the retard amount of the intake valve 21 and the retard amount of the exhaust valve 22 different.

  Further, in the above-described embodiment, when the estimated compression end temperature is lower than the target temperature, the closing timings of the intake valve 21 and the exhaust valve are advanced by the same amount, but the invention is not limited to this. The opening timing of the exhaust valve 22 is 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 or later than the closing timing of the exhaust valve 22 and each of the valves is opened. If the condition that the period sandwiches the compression bottom dead center is maintained, the ECU 100 may make the advance amount of the intake valve 21 and the advance amount of the exhaust valve 22 different.

  Further, in the above-described embodiment, the engine body 10 is a gasoline engine. However, the invention is not limited thereto, and the engine body 10 may be a diesel engine to which a fuel mainly composed of light oil is supplied. In this case, the control of the closing timing of the intake valve 21 and the exhaust valve 22 is applied to the entire operation range of the engine 1. Further, it is not necessary to provide the cylinder block 13 with a spark plug. Further, it is necessary to change the injection timing of the fuel from the fuel injection valve 23 to, for example, near the compression top dead center.

  Further, in the above-described embodiment, the supercharger is the mechanical supercharger 53, but the supercharger may be an electric supercharger if the compressor is configured by a centrifugal blower.

  The above embodiments are merely examples, and the scope of the present disclosure should not be interpreted in a limited manner. The scope of the present disclosure is defined by the claims, and all modifications and changes that fall within the equivalent scope of the claims are within the scope of the present disclosure.

  The technology disclosed herein is useful for a two-stroke engine provided with a supercharger in an intake passage.

DESCRIPTION OF SYMBOLS 1 2 stroke engine with a supercharger 10 Engine main body 11 Cylinder 15 Piston 16 Combustion chamber 19 Intake port 20 Exhaust port 21 Intake valve 22 Exhaust valve 30 Intake electric S-VT (intake valve mechanism)
40 Exhaust Electric S-VT (Exhaust Valve Train)
50 intake passage 53 mechanical supercharger (supercharger)
100 ECU (compression end temperature estimation means, control means)
SN4 intake air temperature sensor (outside air temperature detection means)
SN5 Engine water temperature sensor (engine water temperature detection means)
SN6 Oil temperature sensor (oil temperature detecting means)

Claims (5)

A cylinder forming a combustion chamber, a piston fitted into the cylinder, an intake valve opening and closing an intake port arranged above the cylinder, and an exhaust valve opening and closing an exhaust port arranged above the cylinder A two-stroke engine with a supercharger, wherein a supercharger is provided in an intake passage connected to the engine main body.
An intake valve operating mechanism for changing the closing timing of the intake valve,
Compression end temperature estimation means for estimating the gas temperature in the combustion chamber at the compression top dead center,
Control means for controlling the operation of the intake valve operating mechanism,
The engine body performs compression ignition combustion at least when the engine load is lower than a predetermined load.
In the intake valve and the exhaust valve, 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 substantially the same as the closing timing of the exhaust valve, or the exhaust It is configured to be later than the valve closing timing and each valve opening period sandwiches the bottom dead center,
The control means, during the operation of the supercharger, when the estimated compression end temperature estimated by the compression end temperature estimation means is higher than a preset target temperature, the closing timing of the intake valve, A two-stroke engine with a supercharger, wherein the intake valve mechanism is operated to retard the effective compression ratio so as to decrease the effective compression ratio. The two-stroke engine with a supercharger according to claim 1,
Further provided is an exhaust valve mechanism for changing the closing timing of the exhaust valve,
The control means is configured to further control the operation of the exhaust valve mechanism,
Further, the control means may advance the valve closing timing of the intake valve such that the effective compression ratio becomes higher when the estimated compression end temperature is lower than the target temperature during the operation of the supercharger. While operating the intake valve operating mechanism, the exhaust valve is controlled to maintain the condition that the closing timing of the exhaust valve is substantially the same as the closing timing of the intake valve or earlier than the closing timing of the intake valve. A two-stroke engine with a supercharger, wherein the two-stroke engine is configured to operate a valve mechanism. The two-stroke engine with a supercharger according to claim 1 or 2,
The compression end temperature estimating means is configured to estimate a compression end temperature in consideration of an engine load,
A two-stroke engine with a supercharger, wherein the control means is configured to operate the intake valve operating mechanism so as to delay the closing timing of the intake valve as the engine load increases. The two-stroke engine with a supercharger according to any one of claims 1 to 3,
An outside air temperature detecting means for detecting an outside air temperature;
Engine water temperature detection means for detecting the temperature of the engine cooling water of the engine body,
Oil temperature detecting means for detecting the temperature of the engine oil of the engine body,
The compression end temperature estimating unit estimates the compression end temperature in consideration of the detection results of the outside air temperature detection unit, the engine water temperature detection unit, and the oil temperature detection unit, and the effective compression ratio of the engine body. A two-stroke engine with a supercharger, characterized in that: The two-stroke engine with a supercharger according to any one of claims 1 to 4,
The intake valve operating mechanism is a phase-type valve operating mechanism that changes both the opening timing and the closing timing of the intake valve in an interlocked manner while keeping the opening period of the intake valve constant. 2-stroke engine with supercharger.

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