JP2007205181A - Four cycle internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make transition between self ignition combustion and spark ignition combustion smooth and stabilize combustion. <P>SOLUTION: In a four cycle gasoline engine 1 provided with a spark plug provided with facing a combustion chamber 5, and a variable valve gear 11 capable of varying open close timing of an exhaust valve 10, and capable of spark ignition combustion in which air fuel mixture in the combustion chamber 5 is ignited and burned by ignition of the spark plug 10 and self-ignition combustion in which air fuel mixture is self-ignited and burned, the spark plug 10 is operated in all combustion range of spark ignition combustion range in which spark ignition combustion is possible and self-ignition combustion range in which self-ignition combustion is possible, and variable quantity of the variable valve gear 11 is continuously changed at least in a boundary region in which self-ignition combustion region and spark ignition combustion region are changed over. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a four-cycle internal combustion engine capable of both self-ignition combustion and spark ignition combustion.

In the four-cycle internal combustion engine, an internal combustion engine has been developed that can perform both self-ignition combustion, which has an advantage such as low generation of NOx, and spark ignition combustion that provides high output. In order to realize self-ignition combustion, it is necessary to increase the in-cylinder temperature (for example, about 1000 Kelvin or more in a gasoline engine) and a high compression ratio. To increase the in-cylinder temperature, internal EGR (internal exhaust gas recirculation) ) May be used.
In a four-cycle internal combustion engine capable of self-ignition combustion and spark-ignition combustion, and in which self-ignition combustion increases the in-cylinder temperature by internal EGR, the variable valve mechanism operates the operating periods and valves of the intake and exhaust valves. By changing the lift amount, the overlap of the intake / exhaust valves is controlled, and conditions suitable for the self-ignition combustion and the spark ignition combustion are established.

More specifically, in spark ignition combustion, the intake valve is opened before the top dead center of the piston and the exhaust valve is closed after the top dead center of the piston to overlap the opening period of the intake and exhaust valves (hereinafter referred to as plus overlap). In some cases, this allows efficient intake and exhaust (in other words, less residual gas) and high output.
On the other hand, in self-ignition combustion, the valve opening periods of the intake valve and the exhaust valve do not overlap (hereinafter referred to as minus overlap). The amount of EGR is increased to limit the amount of fresh air flowing, thereby increasing the working gas temperature of the next cycle. Further, the effective compression ratio is increased by setting the intake valve close timing near the bottom dead center, thereby increasing the pressure near the compression top dead center as much as possible. Thereby, both the in-cylinder temperature and the in-cylinder pressure are set to a level at which self-ignition occurs stably, and an atmosphere in which self-ignition combustion occurs stably is formed.
Conventionally, the self-ignition combustion region and the spark ignition combustion region are completely divided based on appropriate parameters (for example, required output). In the self-ignition combustion region, the intake / exhaust valve is controlled to minus overlap and the spark plug is operated. In the spark ignition combustion region, the intake / exhaust valve is controlled to a positive overlap and the spark plug is operated (see, for example, Patent Document 1). FIG. 5 is a diagram showing a change in the mass ratio between the fresh air in the cylinder and the residual gas with respect to the engine load when the overlap is ideally switched by this conventional method.
It is.
JP 2000-320333 A

However, it is not easy to completely separate the self-ignition combustion region and the spark ignition combustion region as in the prior art, and to control the compression ratio and the internal EGR amount according to each combustion mode.
For example, because the boundary of the combustion mode changes variously due to disturbances, it is difficult to set a boundary that secures the auto-ignition combustion region as much as possible, so it is necessary to set a boundary that widens the spark ignition combustion region. Therefore, the auto-ignition combustion area was narrowed.

In addition, since the combustion mode changes abruptly by switching control between self-ignition combustion and spark ignition combustion, it becomes difficult to maintain the same output characteristics and drivability before and after switching. Furthermore, when changing from the optimal control specification for self-ignition combustion to the optimal control specification for spark ignition combustion, the physical conditions change instantaneously, so a response is required to optimize the combustion state near the boundary. A highly reliable control system is required, resulting in an increase in size and cost of the apparatus.
Therefore, the present invention provides a four-cycle internal combustion engine that can be easily controlled, can smoothly shift between the combustion modes of self-ignition combustion and spark ignition combustion, can stably stabilize the combustion, and can expand the self-ignition combustion region. Is.

The four-cycle internal combustion engine according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 includes a spark ignition device (for example, a spark plug 10 in an embodiment to be described later) provided in a combustion chamber (for example, a combustion chamber 5 in an embodiment to be described later), an intake / exhaust valve ( For example, a variable valve mechanism (for example, a variable valve mechanism 11 in an embodiment described later) capable of changing at least one of the opening / closing timing and the lift amount of the exhaust valve 9) in an embodiment described later, A 4-cycle internal combustion engine capable of performing spark ignition combustion in which an air-fuel mixture in the combustion chamber is ignited and combusted by ignition of a spark ignition device, and self-ignition combustion in which the air-fuel mixture is compressed and ignited (for example, an embodiment described later) In the gasoline engine 1), the spark point in all the combustion regions of the spark ignition combustion region where the spark ignition combustion is possible and the self ignition combustion region where the self ignition combustion is possible Actuates the device, at least the self-ignition combustion region and the spark-ignition combustion region is switched boundary region, characterized in that continuously changing a variable amount of the variable valve mechanism.
With this configuration, the internal EGR rate can be continuously changed even in the boundary region where the self-ignition combustion region and the spark ignition combustion region are switched, and mixing is performed prior to the self-ignition combustion in the boundary region. Spark ignition combustion can be generated in a part of the air, whereby the temperature of the air-fuel mixture is raised to establish the self-ignition combustion condition, and the self-ignition combustion of the entire air-fuel mixture can be reliably caused.

According to a second aspect of the present invention, in the first aspect of the present invention, in the self-ignition combustion region and the boundary region, the fuel injection amount is controlled so that the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes substantially the stoichiometric air-fuel ratio. It is characterized by doing.
By setting the air-fuel ratio in the self-ignition combustion region to the stoichiometric air-fuel ratio, self-ignition combustion can be stably generated.
The boundary region is a region in which the combustion form is uncertain, and both self-ignition combustion and spark ignition combustion can occur. However, by setting the air-fuel ratio to the stoichiometric air-fuel ratio (stoichiometric) in this boundary region, auto-ignition combustion or Both combustions of spark ignition combustion can be made possible.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the variable valve mechanism is provided only in the exhaust valve.
With this configuration, the internal EGR rate (EGR amount) can be changed only by controlling the operation of the exhaust valve by the variable valve mechanism without performing any special control on the operation of the intake valve.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the flow of gas from the intake passage to the combustion chamber is permitted in the intake passage upstream of the intake valve, and the flow from the combustion chamber to the intake passage is allowed. A one-way valve (for example, an intake reed valve 14 in an embodiment to be described later) for preventing gas flow is provided.
With this configuration, it is possible to prevent the gas from flowing backward from the combustion chamber to the intake passage even when the opening period of the intake valve and the exhaust valve is set to minus overlap. Can be protected. Further, since exhaust gas can be prevented from escaping from the combustion chamber to the intake passage side, heat outflow can be prevented.

According to the first aspect of the present invention, it is not necessary to change the engine control rapidly in the boundary region, the combustion can be stabilized in the boundary region, and the transition between the self-ignition combustion and the spark ignition combustion is smooth. Can be done. In addition, the self-ignition combustion can be utilized to the maximum, and the self-ignition combustion area can be expanded, so that the advantages of the self-ignition combustion can be utilized to the maximum.
According to the invention of claim 2, stable combustion can be obtained in the self-ignition combustion region and the boundary region.

According to the invention of claim 3, since the internal EGR rate can be changed only by controlling the operation of the exhaust valve, the valve operating mechanism can be simplified, and the 4-cycle internal combustion engine can be reduced in size and weight. Can be.
According to the fourth aspect of the present invention, it is possible to prevent the gas from flowing backward from the combustion chamber to the intake passage, so that the intake system can be protected. Further, since the exhaust gas is not escaped from the combustion chamber to the intake passage side, heat outflow can be prevented, and as a result, self-ignition combustion is likely to occur.

Embodiments of a four-cycle internal combustion engine according to the present invention will be described below with reference to the drawings of FIGS.
The four-cycle internal combustion engine in this embodiment is a four-cycle gasoline engine. As shown in the system configuration diagram of FIG. 1, a four-cycle gasoline engine (hereinafter abbreviated as engine) 1 includes a cylinder block 2, a cylinder head 3, The piston 4 and the combustion chamber 5 formed so as to be surrounded by the piston 4 are provided, and the reciprocating motion of the piston 4 is converted into the rotational motion of the crankshaft 32 through the connecting rod 31.

  The cylinder head 3 includes an intake valve 7 for opening and closing an intake port (intake passage) 6 communicating with the combustion chamber 5, an exhaust valve 9 for opening and closing an exhaust port (exhaust passage) 8 communicating with the combustion chamber 5, and a combustion chamber. A spark plug (spark igniter) 10 and a fuel injection valve 12 that are disposed facing 5 are provided. That is, the engine 1 is configured as a so-called in-cylinder direct injection engine that directly injects fuel into the cylinder. The intake valve 7 and the exhaust valve 9 can be opened and closed independently by a valve operating mechanism. In particular, in this embodiment, the intake valve 7 is constituted by a valve mechanism 33 whose opening / closing timing cannot be changed, but the exhaust valve 9 is provided with a variable valve mechanism 11, and the valve closing timing of the exhaust valve 9 is changed. Have been able to.

  The intake port 6 is provided with a throttle valve 13 whose opening degree is controlled in accordance with the amount of depression of an accelerator pedal (not shown) or the amount of rotation of the throttle grip. Further, an intake reed valve (one-way valve) that permits the gas flow from the intake port 6 to the combustion chamber 5 and prevents the gas flow from the combustion chamber 5 to the intake port 6 to the intake port 6 downstream of the throttle valve 13. Directional valve) 14 is provided.

  The engine 1 also includes an engine electronic control unit (ENG-ECU, hereinafter abbreviated as “ECU”) 20. The ECU 20 controls the throttle opening degree sensor 21 that detects the opening degree of the throttle valve 13 and the rotational speed of the crankshaft 32. A rotation speed sensor 22 for detecting, an air-fuel ratio sensor 23 for detecting the air-fuel ratio (A / F) of the gas in the combustion chamber 5, an intake air temperature sensor 24 for detecting the temperature of the intake air flowing through the intake port 6, and the exhaust port 8 Output signals of sensors such as an exhaust temperature sensor 25 for detecting the exhaust temperature of the engine, an in-cylinder pressure sensor 26 for detecting the in-cylinder pressure (or pressure in the intake manifold), a crank angle sensor 27 for detecting the rotation angle of the crankshaft 32, and the like. Entered. The ECU 20 determines the operating state of the engine 1 based on input signals from these sensors, and performs predetermined control such as ignition timing control, fuel injection amount control, and internal EGR rate control.

  The engine 1 is capable of spark ignition combustion in which the air-fuel mixture in the combustion chamber 5 is ignited and combusted by ignition by the spark plug 10 and self-ignition combustion in which the air-fuel mixture in the combustion chamber 5 is compressed and ignited. In addition, the engine specifications are set. Self-ignition combustion is performed in the low load region of the engine 1, and spark ignition combustion is performed mainly in the medium / high load region of the engine 1. In this engine 1, the variable valve mechanism 11 is controlled so that the valve closing timing of the exhaust valve 9 is advanced as the load decreases, thereby increasing the internal EGR amount (internal EGR rate) in the low load region. Thus, the temperature of the mixed gas (the working gas temperature) in the combustion chamber 5 is increased to enable self-ignition combustion.

However, in the engine 1, the self-ignition combustion region in which self-ignition combustion is possible and the spark ignition combustion region in which spark-ignition combustion is possible are not clearly distinguished and controlled as in the past. This is the main feature of the engine 1 and the following configuration is adopted.
(1) In the boundary region where the self-ignition combustion and the spark ignition combustion are switched, the variable valve mechanism 11 performs control for continuously changing the valve closing timing of the exhaust valve 9.
(2) Ignition control for operating the spark plug 10 is executed in all combustion regions of the self-ignition combustion region and the spark ignition combustion region.

  The configuration (1) will be described in detail. As is well known, in general, an internal combustion engine needs to efficiently perform intake and exhaust in order to obtain a high output. An overlap is provided during the valve opening period. In the engine 1 as well, an overlap is provided in the opening period of the intake valve 7 and the exhaust valve 9 in the spark ignition combustion region corresponding to the middle / high load region.

  On the other hand, in order to generate self-ignition combustion, the temperature of the air-fuel mixture in the combustion chamber 5 needs to be increased, and the engine 1 uses the internal EGR to increase the temperature of the air-fuel mixture. In order to increase the internal EGR amount (internal EGR rate) in the self-ignition combustion region, as shown in FIG. 2, the valve closing timing of the exhaust valve 9 is advanced and the opening period of the intake valve 7 and the exhaust valve 9 is increased. The overlap is eliminated, and the negative overlap is increased as the load of the engine 1 is lowered to increase the internal EGR rate.

  In particular, in the engine 1, the valve closing timing of the exhaust valve 9 is continuously advanced as the load decreases even in the boundary region where the self-ignition combustion and the spark ignition combustion are switched. In the boundary region from the load side to the high load side in the self-ignition combustion region, the internal EGR rate (internal EGR amount) can be continuously increased. As a result, it is not necessary to perform control to change the valve closing timing of the exhaust valve 9 abruptly in the self-ignition combustion region and the spark ignition combustion region, and the control of the exhaust valve 9 is not complicated. Control of the closing timing of the exhaust valve 9 is executed by the ECU 20 via the variable valve mechanism 11.

  FIG. 3 is a diagram conceptually showing an example of a change in the mass ratio of fresh air and residual gas charged in the cylinder (that is, in the combustion chamber 5) with respect to the load of the engine 1. In the example, the internal EGR rate is changed in all combustion regions (in other words, full load region) of the self-ignition combustion region (AI combustion region) and the spark ignition combustion region (SI combustion region). In this case, however, the spark ignition combustion region is set within the range of the internal EGR rate at which spark ignition combustion occurs.

  In addition, since the intake reed valve 14 is provided in the intake port 6, even when the opening period of the intake valve 7 and the exhaust valve 9 is set to minus overlap, gas flows from the combustion chamber 5 to the intake port 6. Backflow can be prevented and the intake system can be protected. Further, since exhaust gas can be prevented from escaping from the combustion chamber 5 to the intake port 6 side, the outflow of heat can be prevented and self-ignition combustion can be easily generated.

  Further, in this embodiment, the variable valve mechanism 11 is provided only in the exhaust valve 9, and the internal EGR rate (internal EGR amount) is changed only by advance control of the closing timing of the exhaust valve 9. The intake valve 7 is not provided with a variable valve mechanism, and the opening / closing timing of the intake valve 7 is not specially controlled. Therefore, the valve operating mechanism can be simplified, and the engine 1 can be reduced in size and weight.

  The configuration (2) will be described in detail. With this configuration, a spark based on the operation of the spark plug 10 is generated regardless of the combustion region (in other words, in the full load region of the engine 1). This spark is a so-called “abandoned fire” that does not contribute to combustion when the self-ignition combustion condition is satisfied in the self-ignition combustion region, and when the spark ignition combustion condition is satisfied in the spark-ignition combustion region, Stable spark ignition combustion is generated throughout the mixture. Further, in the boundary region where the self-ignition combustion and the spark ignition combustion are switched, the ignition timing of the spark plug 10 is set to advance from the self-ignition timing, so that the spark ignition combustion occurs in a part of the air-fuel mixture prior to the self-ignition combustion. Thus, the temperature of the air-fuel mixture can be raised to establish the self-ignition combustion condition, and the self-ignition combustion of the entire air-fuel mixture can be generated.

Further, by setting the ignition timing of the spark plug 10 to be more advanced than the self-ignition timing, it is possible to ignite near the ideal ignition timing in the spark ignition combustion even when the ignition plug 10 is completely switched to the spark ignition combustion. In addition, it is not necessary to perform control to change the ignition advance angle rapidly in the boundary region. As a result, ignition control is not complicated, and the control device can be downsized.
It is preferable that the advance timing of the ignition timing is set so as to be continuously connected, for example, as the load decreases from the ignition timing in the high load spark ignition combustion region. Note that the ignition timing may be set constant in the low-load self-ignition combustion region.

  Therefore, by adopting the configurations (1) and (2), it is not necessary to change the control of the engine 1 abruptly in the boundary region, and combustion can be stabilized in the boundary region. The transition of spark ignition combustion becomes smooth. In addition, since the self-ignition combustion can be used to the maximum and the auto-ignition combustion area can be expanded, the NOx reduction in the exhaust gas, which is an advantage of the self-ignition combustion, can be used to the maximum.

Next, the air-fuel ratio (A / F) in the self-ignition combustion region and the boundary region will be considered.
The air-fuel ratio in the self-ignition combustion region is preferably a stoichiometric air-fuel ratio (stoichiometric) in order to stably generate self-ignition combustion. On the other hand, in spark ignition combustion, the fuel injection amount can be changed according to the fuel consumption and the required output, so the air-fuel ratio is flexible.
The boundary region is an indeterminate combustion mode, and both self-ignition combustion and spark ignition combustion can occur. However, if the air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric), either auto-ignition combustion or spark ignition combustion Can also occur. Therefore, it is preferable to set the air-fuel ratio in the boundary region to the stoichiometric air-fuel ratio (stoichiometric).
In addition, although the engine load is a spark ignition combustion region in the middle and high load regions, setting the air-fuel ratio leaner than the stoichiometric air-fuel ratio in the middle load region optimizes the fuel consumption rate as an internal combustion engine. Preferred above.

Note that the definition of the air-fuel ratio when the internal EGR is performed does not take into account the residual gas amount (internal EGR gas amount) in the cylinder, but the amount of fresh air (mass) and the amount of fuel injection (mass). Is the ratio.
When the internal EGR is not performed, generally, based on the opening of the throttle valve 13 detected by the throttle opening sensor 21 (hereinafter abbreviated as the throttle opening) and the engine speed detected by the rotation speed sensor 22. Although the fuel injection amount is calculated from the three-dimensional map, when the internal EGR is performed by the variable valve control in the engine 1, the throttle opening is performed according to the variable valve control map as shown in Expression (1). The fuel injection amount is set according to the actual fresh air intake amount at the air-fuel ratio and the corrected throttle opening. In this embodiment, as described above, the air-fuel ratio in the auto-ignition combustion region and the boundary region is the stoichiometric air-fuel ratio.
(Throttle opening after correction) = (VT coefficient) × (actual throttle opening) (1)
Here, the VT coefficient is a coefficient obtained from the variable valve control map, and has a correlation with the EGR rate. Depending on the required EGR rate, the variable valve control map is prepared in advance with the rotational speed and actual throttle opening as parameters.
For example, comparing the case where the internal EGR rate is 0% and the case where it is 50%, the actual fresh air intake amount is smaller in the latter than in the former, so the VT coefficient when the internal EGR rate is 50% is the internal EGR rate. Is smaller than the VT coefficient at 0%.

  The internal EGR rate is calculated by the ECU 20 based on the operating state of the engine 1. That is, the ECU 20 detects the engine speed detected by the speed sensor 22, the fuel injection amount calculated from the map based on the throttle opening and the engine speed, and the air-fuel ratio detected by the A / F sensor 23. The intake air temperature detected by the intake air temperature sensor 24, the exhaust gas temperature detected by the exhaust gas temperature sensor 25, and the combustion chamber 5 when the intake valve is closed calculated based on the crank angle detected by the crank angle sensor 27. The cylinder residual gas amount (internal EGR gas amount) is estimated and calculated based on the volume and the cylinder pressure at the end of intake detected by the cylinder pressure sensor 26 when the intake valve is closed, and based on this, the internal EGR rate is calculated. Is calculated. For calculating the internal EGR rate, the internal EGR rate is obtained at the test stage, and the variable valve control map is set so that this becomes the required internal EGR rate.

Generally, it is known that the following correlation exists between the internal EGR rate and parameters (throttle opening, engine speed, valve timing, etc.).
(A) When the valve timing of the intake / exhaust valves is fixed, when the throttle opening is small, the amount of fresh air intake decreases, so the internal EGR rate increases, and when the throttle opening is large, fresh air Since the intake air amount increases, the internal EGR rate decreases.
(B) When the valve timing is set so as to cause self-ignition and the throttle opening is fixed, the internal EGR rate is large because the intake time is shortened and the intake amount of fresh air is reduced when the engine speed is large. Thus, when the engine speed is small, the intake time becomes longer and the intake amount of fresh air increases, so the internal EGR rate becomes smaller.
(C) When the throttle opening is fixed, when the intake valve opening period (crank angle) is small, the amount of fresh air intake decreases, so the internal EGR rate increases, and the intake valve opening period ( When the crank angle) is large, the amount of fresh air increases, so the internal EGR rate decreases.
When the exhaust valve opening period (crank angle) is small, exhaust from the cylinder decreases, so the internal EGR rate increases. When the exhaust valve opening period (crank angle) is large, exhaust from the cylinder Since it increases, the internal EGR rate decreases.

By the way, when the engine speed is high, the engine is required to have a high output. However, in the correlation with the internal EGR rate, the internal EGR rate becomes large when the engine speed is large, and the high output is maintained with the self-ignition combustion. It becomes difficult to generate. In addition, when the engine speed is low and the load is low, it is a self-ignition combustion region. Therefore, the transition of self-ignition combustion / spark ignition combustion can be smoothly performed by using continuous control of internal EGR rate by variable valve control together with appropriate throttling (control of throttle valve by electronic control, etc.). Is possible. Further, the fuel injection timing by direct fuel injection in the cylinder is also a control element.
Further, for example, the opening period of the exhaust valve 9 is increased and controlled so that a high output can be generated by increasing the intake amount of fresh air and decreasing the internal EGR rate when the engine speed is high, Supercharging is performed, the opening degree of the throttle valve 13 is actively controlled to increase, or external EGR is performed to widen the auto-ignition combustion range. Examples of supercharging means include turbochargers, superchargers, resonance inertia supercharging, ram pressure supercharging, and the like.

[Other Examples]
The present invention is not limited to the embodiment described above.
For example, in the above-described embodiment, the internal EGR rate is changed by the closing timing control of the exhaust valve 9, but a variable valve mechanism 11 capable of changing and controlling both the closing timing and the lift amount of the exhaust valve 9 is prepared. Thus, the internal EGR rate can be changed by executing the lift amount control of the exhaust valve 9 together with the valve closing timing control of the exhaust valve 9.
The intake valve 7 can also be provided with a variable valve mechanism to control the operation of the intake valve 7 to change the internal EGR rate.
Furthermore, as shown in FIG. 4, two types of exhaust valves, a main exhaust valve and an auxiliary exhaust valve, are installed for one cylinder, and the main exhaust valve changes the opening / closing timing in the same manner as the intake valve 7 of the above-described embodiment. The main exhaust valve is always opened and closed at the same timing in all areas from the self-ignition combustion area to the spark ignition combustion area, and the auxiliary exhaust valve is opened and closed only in the self-ignition combustion area and the boundary area. In addition, the internal EGR rate may be changed by overlapping the valve opening period with the valve opening period of the intake valve, making the valve opening period variable, and controlling the valve opening period of the auxiliary exhaust valve.

1 is a system configuration diagram in one embodiment of a four-cycle internal combustion engine according to the present invention. FIG. It is a figure which shows the valve timing of the intake / exhaust valve of the said 4-cycle internal combustion engine. FIG. 3 is a conceptual diagram showing a change in a mass ratio of residual gas and fresh air with respect to a load in the four-cycle internal combustion engine. It is a figure which shows the valve timing of the intake / exhaust valve in other Examples of the 4-cycle internal combustion engine which concerns on this invention. It is a figure which shows the change of the mass ratio of the fresh air in a cylinder with respect to an engine load, and residual gas when an overlap is switched ideally by the conventional method.

Explanation of symbols

1 Gasoline engine (4-cycle internal combustion engine)
5 Combustion chamber 6 Intake port (intake passage)
7 Intake valve 8 Exhaust port (exhaust passage)
9 Exhaust valve 10 Spark plug (spark ignition device)
11 Variable valve mechanism 14 Intake reed valve (one-way valve)

Claims (4)

A spark ignition device provided facing the combustion chamber, and a variable valve mechanism capable of changing at least one of the opening and closing timings and the lift amount of the intake and exhaust valves, and the combustion by the ignition of the spark ignition device In a four-cycle internal combustion engine capable of spark ignition combustion for igniting and burning an air-fuel mixture in a room and self-ignition combustion for compressing and igniting the air-fuel mixture,
The spark ignition device is operated in all the combustion regions of the spark ignition combustion region capable of spark ignition combustion and the self ignition combustion region capable of self ignition combustion, and at least the self ignition combustion region and the spark ignition combustion. A four-cycle internal combustion engine characterized by continuously changing the variable amount of the variable valve mechanism in a boundary region where the region is switched.   2. The four-cycle internal combustion engine according to claim 1, wherein the fuel injection amount is controlled so that the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes substantially the stoichiometric air-fuel ratio in the self-ignition combustion region and the boundary region.   The four-cycle internal combustion engine according to claim 1 or 2, wherein the variable valve mechanism is provided only in an exhaust valve.   The one-way valve for permitting the gas flow from the intake passage to the combustion chamber and preventing the gas flow from the combustion chamber to the intake passage is provided in the intake passage upstream of the intake valve. The four-cycle internal combustion engine according to claim 2.

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