JP2006161584A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent fuel adherence to a wall face of a combustion chamber by increasing an intake air flow from a side where a wall part of an intake valve around a valve seat is not provided and generating a high-speed directional intake air flow. <P>SOLUTION: In this internal combustion engine capable of changing valve lift amount of the intake valve 2 in accordance with engine load, a wall part 10 along the intake valve lift direction is formed on an upper wall face 5 of the combustion chamber 4 in the vicinity of the valve seat 6 of the intake valve 2 relatively in an intake air introduction direction side. In an operating condition where the lift amount of the intake valve 2 becomes extremely small, a clearance between the intake valve 2 and the wall part 10 is set larger than the extremely small lift amount, and in an operating condition where the lift amount of the intake valve 2 becomes small, the clearance between the intake valve 2 and the wall part 10 is set smaller than the small lift amount. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine in which a valve lift amount of an intake valve is variable according to an engine load.

In Patent Document 1, in an internal combustion engine having means for controlling the lift and / or opening period of an intake valve, a wall adjacent to the valve seat and the intake flow direction in the intake valve and / or the intake port, The cross-section of the intake flow that can use the flow is reduced at least in the angular region centered on the motion axis of the intake valve, so that a small directional valve lift is formed to produce a high-speed directional intake flow. It is disclosed.
JP-A-9-112284

  However, in Patent Document 1, when the valve lift characteristic of the intake valve is changed according to the engine load, if the intake air amount is controlled by minimizing the intake valve lift during idling, the intake air Since the intake air flows along the combustion chamber wall surface from the side where the wall around the valve seat is not provided, fuel adheres to the spark plug, exhaust valve, combustion chamber wall surface, cylinder bore, and unburned HC is discharged. There is a risk that.

  Therefore, the present invention provides an internal combustion engine capable of changing the valve lift amount of the intake valve in accordance with the engine load, on the upper wall surface of the combustion chamber that is near the valve seat of the intake valve and relatively on the intake introduction direction side. In the state where a wall portion is formed along the intake valve lift direction and the lift amount of the intake valve is a predetermined first lift amount, the clearance between the intake valve and the wall portion is larger than the first lift amount, In a state where the intake valve is in a second lift amount in which the lift amount is relatively larger than the predetermined first lift amount, the intake valve and the wall are set so that the second lift amount is larger than the clearance between the intake valve and the wall portion. It is characterized by a clearance with the part. Thus, in a state where the lift amount of the intake valve becomes the first lift amount, the intake flow from the side where the wall portion around the valve seat of the intake valve is provided is increased, and the wall portion around the valve seat of the intake valve Reduces the intake air flow from the side where is not provided. In addition, in the state where the lift amount of the intake valve is the second lift amount, the intake flow from the side where the wall portion around the valve seat of the intake valve is provided is reduced, and the wall portion around the valve seat of the intake valve is reduced. The intake air flow from the side not provided increases.

  According to the present invention, in the state where the lift amount of the intake valve is the first lift amount, the fuel adhering to the combustion chamber wall surface is reduced by utilizing the rectification effect of the intake flow by the wall portion, and the lift amount of the intake valve In a state where the second lift amount is reached, the intake flow from the side where the wall portion around the valve seat of the intake valve is not provided can be increased, and a high-speed directional intake flow can be generated.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  Each embodiment described below is based on an internal combustion engine including a variable valve mechanism that can continuously vary the valve lift amount of the intake valve according to the engine load. The valve lift amount is controlled to be smaller than that during high load, and the lift amount is controlled to be even smaller during idle operation. Further, by controlling the valve lift amount of the intake valve in the minimum lift region, it is possible to perform engine load control without performing precise control of the throttle opening. The variable valve mechanism that can change the valve lift characteristic of the intake valve is already known from Japanese Patent Application Laid-Open No. 11-107725 previously proposed by the present applicant. Description is omitted.

  FIG. 1 is an explanatory view schematically showing the internal combustion engine according to the first embodiment of the present invention, showing the shape of the combustion chamber of the internal combustion engine viewed from the piston side, in other words, the shape of the combustion chamber on the cylinder head side. It is explanatory drawing.

  The cylinder head 1 is provided with two intake valves 2 that are controlled to open and close so that the valve lift amount is variable according to the engine load, and two exhaust valves 3 are arranged per cylinder. Yes.

  The intake valve 2 and the exhaust valve 3 are respectively connected to an intake valve valve seat 6 and an exhaust valve valve seat 7 arranged on an upper wall surface 5 of a pent roof type combustion chamber 4 (see FIGS. 2 and 3 to be described later). Sit down.

  The intake valve valve seat 6 is provided at a connection portion between an intake port 8 (see FIGS. 2 and 3 described later) formed in the cylinder head 1 and the combustion chamber 4. The exhaust valve valve seat 7 is provided at a connection portion between an exhaust port 9 (see FIGS. 2 and 3 described later) formed in the cylinder head 1 and the combustion chamber 4.

  The upper wall surface 5 of the combustion chamber 4 is formed with a wall portion 10 that partially surrounds the periphery of the intake valve valve seat 6. This wall portion 10 protrudes along the intake valve lift direction on the outer peripheral side of a portion (the right half in FIG. 1 of the intake valve valve seat 6) that is relatively on the intake introduction direction side of the intake valve seat 6. It is formed to do.

  Here, the intake air introduction direction is specifically the right side in the left-right direction in FIG. This is because the intake port 8 is connected to the combustion chamber 4 from the right side in FIG. 1 with respect to the center of the combustion chamber 4, and the opening of the intake port 8 to the combustion chamber 4 is located on the right side in FIG. This is because the portion is relatively positioned on the side where the intake air is introduced. Therefore, in the upper wall surface 5 of the combustion chamber 4, the right side in the left-right direction in FIG. 1 is defined as the intake air introduction direction, and the left side in the left-right direction in FIG.

  2 and 3 are cross-sectional views taken along the line AA in FIG. 1. FIG. 2 shows the idle operation state after warm-up in which the valve lift amount of the intake valve 2 is a minimum lift, and FIG. The low load operation state excluding the idle operation after warm-up in which the valve lift amount of the valve 2 is a small lift is shown.

  The wall portion 10 described above will be described in detail. In the first embodiment, as is apparent from FIGS. 2 and 3, in the idle operation state after the warm-up in which the valve lift amount of the intake valve 2 is the minimum lift, The clearance Q between the side surface 11a of the valve head 11 of the intake valve 2 and the wall surface 10a of the wall portion 10 protruding from the upper wall surface 5 of the combustion chamber 4 becomes larger than the lift amount (minimum lift amount P) at this time, In a low-load operation state excluding warm-up idle where the valve lift amount of the intake valve 2 is a small lift, the side surface 11a of the valve head 11 of the intake valve 2 and the wall portion 10 protruding from the upper wall surface 5 of the combustion chamber 4 The clearance Q with the wall surface 10a is set to be smaller than the lift amount (small lift amount R) at this time.

  In other words, the substantial intake valve opening area on the intake introduction direction side when the intake valve is minimally lifted is relatively larger than the substantial intake valve opening area on the intake introduction direction side when the intake valve is small lifted. The substantial intake valve opening area on the anti-intake introduction direction side when the valve is minimally lifted is set to be relatively smaller than the substantial intake valve opening area on the anti-intake introduction direction side during the small intake valve lift. ing.

  The height M of the wall surface 10a of the wall 10 facing the side surface 11a of the valve head 11 of the intake valve 2, that is, the protrusion amount M of the wall 10 in the valve lift direction is based on the intake valve 2 seating position. It is set to be slightly larger than the lift amount (small lift amount R) in the low-load operation state excluding the idle after warm-up. In other words, in the state where the valve lift amount of the intake valve 2 is a small lift compared to the state where the valve lift amount of the intake valve 2 is a minimal lift, the combustion chamber 4 is located more than the lower surface position of the valve head 11 of the intake valve 2. The protruding amount of the wall portion 10 protruding inward (piston side) is set to be small. The height of the wall portion 10 (the height M of the wall surface 10a) may be approximately the same as the small lift amount R.

  In the first embodiment, when the intake valve is small lifted (during low-load operation excluding idle after warm-up), the substantial intake valve opening area on the intake introduction direction side where the wall portion 10 is provided is By relatively reducing the intake valve as compared with the minimum lift, the intake flow flowing into the combustion chamber 4 from the intake introduction direction where the wall portion 10 is provided in the intake valve opening is relatively reduced, and the intake air Of the valve opening, the intake air flowing into the combustion chamber 4 from the side opposite to the intake intake direction where the wall 10 is not provided is relatively increased, and combustion from the side opposite to the intake intake direction of the intake valve opening is performed. A tumble flow having an intake flow flowing into the chamber 4 as a main flow is generated in the combustion chamber 4 (see FIG. 3).

  At this time, the intake air flow that flows into the combustion chamber 4 from the intake valve opening side of the intake valve opening has a large flow velocity and a sufficient valve lift amount, so that the intake valve flows along the upper wall surface 5 of the combustion chamber 4. Flow away from the upper wall surface 5 of the combustion chamber 4 rather than from the piston (not shown), and flows into the spark plug 12, the exhaust valve 3, the upper wall surface 5 of the combustion chamber 4, and the cylinder bore 13. It is possible to prevent a large amount of fuel from adhering and to prevent a large amount of unburned HC from being discharged.

  On the other hand, when the intake valve is minimally lifted (idle state after warm-up), the valve lift amount of the intake valve 2 is further reduced compared to when the intake valve is slightly lifted, and the intake flow velocity during the intake stroke is greater than that during the intake valve small lift. The intake flow that becomes larger and flows into the combustion chamber 4 from the side opposite to the intake air introduction side in the intake valve opening portion flows along the upper wall surface 5 of the combustion chamber 4.

  However, in the first embodiment, at the time of the intake valve minimal lift, the wall surface 10a of the wall 10 rectifies the intake flow flowing into the combustion chamber 4 from the intake introduction direction side of the intake valve opening without being obstructed. The intake flow flowing into the combustion chamber 4 (piston direction) from the intake introduction direction side in the intake portion opening is relatively increased.

  That is, the substantial intake valve opening area on the intake intake direction side is larger than the substantial intake valve opening area on the anti-intake introduction direction side. The intake flow decreases, the intake flow from the intake valve opening portion relatively increases from the intake introduction direction side, and the intake flow that flows into the combustion chamber 4 from the intake valve introduction portion side of the intake valve opening portion becomes the main flow. A tumble flow is generated in the combustion chamber 4 (refer to FIG. 2).

  That is, the wall portion 10 formed around the intake valve valve seat 6 reduces the intake flow flowing into the combustion chamber 4 from the side opposite to the intake direction in the intake valve opening during the intake valve minimum lift. The amount of fuel adhering to the upper wall surface 5 of the combustion chamber 4 is reduced, and a large amount of unburned HC is prevented from being discharged.

  Further, the height M of the wall surface 10a of the wall portion 10 is set to be slightly larger than the lift amount (small lift amount R) in the low load operation state excluding the idle after the warm-up with reference to the intake valve 2 seating position. Therefore, there is no interference when the engine load is high or medium load.

  Hereinafter, other embodiments of the present invention will be sequentially described. However, the same reference numerals are given to components common to the above-described first embodiment, and redundant description will be omitted.

  4 to 9 show a second embodiment of the present invention. As shown in FIG. 4, the second embodiment has a wall portion only for one of the two intake valves 2 and 2 in the same cylinder in the internal combustion engine of the first embodiment described above. 10 is formed. In other words, in the second embodiment, in the internal combustion engine of the first embodiment described above, only one of the two intake valves 2, 2 in the same cylinder is close to the wall 10. It has been made.

  For convenience of explanation, the intake valve 2 in which the wall portion 10 is provided on the outer peripheral side of the portion of the corresponding intake valve valve seat 6 that is relatively on the intake introduction direction side is referred to as an intake valve close to the wall portion 10. An intake valve that is not close to the wall portion 10 is the first intake valve 21 and the intake valve 2 that is not provided with the wall portion 10 on the outer peripheral side of the portion of the corresponding intake valve valve seat 6 that is relatively in the intake introduction direction. As a second intake valve 22.

  In the second embodiment, as shown in FIGS. 5 to 8, the valve of the first intake valve 21 at the time of partial load (a low-load operation state excluding the warm-up idle operation and an idle operation state after the warm-up). The lift amount is set to be larger than the valve lift amount of the second intake valve 21.

  Then, as shown in FIG. 9, the side surface 11 a of the valve head 11 of the first intake valve 21 and the combustion chamber 4 in the idle state after warm-up when the valve lift amount of the first intake valve 21 is a minimum lift. The wall portion 10 is set such that the clearance Q between the wall portion 10 protruding from the upper wall surface 5 and the wall surface 10a is larger than the lift amount (minimum lift amount P) of the first intake valve 21 at this time. In the second embodiment, the side surface 11a of the valve head 11 of the first intake valve 21 and the side surface 11a of the first intake valve 21 in the low load operation state except for the idle after warm-up where the valve lift amount of the first intake valve 21 is a small lift, The clearance Q with the wall surface 10a of the wall portion 10 protruding from the upper wall surface 5 of the combustion chamber 4 is set to be smaller than the lift amount (small lift amount R) at this time. That is, the relative relationship between the first intake valve 21 and the wall portion 10 in the second embodiment conforms to the first embodiment described above.

  In such a second embodiment, the same effects as those of the first embodiment described above can be obtained, and the lift amount of the second intake valve 22 is set to the lift amount of the first intake valve 21 at the time of partial load. By reducing the size, the intake flow flowing into the combustion chamber 4 from the first intake valve 21 increases, and the intake flow has directivity by the wall portion 10 provided around the first intake valve 21, so that the inside of the cylinder during the intake stroke The swirl flow of gas is further increased, and the ignitability and combustion state after spark ignition are improved.

  Further, when the first intake valve 21 and the second intake valve 22 are lifted to generate a maximum output, the adverse effect of the increase in the intake resistance due to the wall 10 is minimized, and the intake flow rate from the second intake valve 22 is minimized. Since the decrease can be avoided, there is an advantage that the output can be increased as compared with the first embodiment described above (when both intake valves 2 and 2 are close to the wall portion 10).

  In the second embodiment, the intake air flowing into the combustion chamber 4 from the first intake valve 21 is stopped by stopping the second intake valve 22, that is, zero lift, as shown in FIG. The flow may be further increased. In this case, the swirl strength is further increased and the combustion improvement effect is further increased in the low load operation state except for the idle after warm-up when the valve lift amount of the first intake valve 21 is a small lift. Further, even in the idle operation state after warm-up in which the valve lift amount of the first intake valve 21 is a minimum lift, the intake flow velocity flowing in the piston direction along the wall surface 10a of the wall portion 10 further increases, so the combustion improvement effect is further increased. Increase.

  11 and 12 show a third embodiment of the present invention. In the third embodiment, the portion of the intake valve valve seat 6 on which the first intake valve 21 is seated that is relatively on the side opposite to the intake direction (the view of the intake valve valve seat 6 is the same as the second embodiment described above. 11, the second wall portion 30 is provided on the outer peripheral side of the substantially left half).

  The second wall portion 30 is formed on the upper wall surface 5 of the combustion chamber 4 and protrudes along the lift direction of the first intake valve 21. Moreover, in this 2nd wall part 30, as shown in FIG. 12, the rising part 31 from the upper wall surface 5 exhibits the cross-sectional substantially circular arc shape, and is formed in the shape where it rises smoothly.

  In such a third embodiment, the intake flow from the entire periphery of the first intake valve 21 is rectified and flows in the piston direction, and the intake flow flows along the upper wall surface 5 and the side wall surface of the combustion chamber 4. Therefore, the amount of fuel adhering to the wall surface of the combustion chamber 4 can be reduced as a whole, and the unburned HC emission can be further reduced.

  In addition, since the rising portion 31 of the second wall portion 30 has a substantially arcuate cross section and has a smooth rising shape, the separation of the intake air flow is promoted compared to the case where the rising portion 31 is angular, The intake resistance can be reduced.

  13 to 16 show a fourth embodiment of the present invention. In the fourth embodiment, in the second embodiment described above, the intake valve valve seat 6a on which the first intake valve 21 is seated is located upstream of the intake valve seat 6b on which the second intake valve is seated. The 2nd wall part 30 is formed by arrange | positioning. More specifically, as shown in FIG. 14, the intake valve valve seat 6 a on which the first intake valve 21 is seated moves backward from the upper wall surface 5 of the combustion chamber 4 to the intake upstream side, and the first intake valve 21 is seated. The intake valve seat 6a and the intake valve seat 6b on which the second intake valve 22 is seated are set to be offset in the intake valve lift direction. Then, as the intake valve valve seat 6a on which the first intake valve 21 is seated retreats to the intake upstream side, the second wall 30 is formed on the outer peripheral side of the intake valve valve seat 6a over the entire circumference. Is formed.

  As shown in FIGS. 15 and 16, the second wall 30 in the fourth embodiment has a clearance S between the side surface 11 a of the valve head 11 of the first intake valve 21 and the wall surface 30 a of the second wall 30. It is set to be larger than the lift amount (minimum lift amount P) of the first intake valve 21 at the time of minimum lift of the intake valve (during idle operation after warm-up). Furthermore, the second wall portion 30 in the fourth embodiment is such that the height T from the valve seat 6a for the intake valve on which the first intake valve 21 is seated is the first when the intake valve is minimally lifted (during idle operation after warm-up). The maximum lift amount (maximum small lift amount) of the first intake valve 21 that is larger than the lift amount (minimum lift amount P) of the single intake valve 21 and that is small when the intake valve is small (during low-load operation excluding idle after warm-up) Rmax).

  Note that the wall surface 30a of the second wall portion 30 in the fourth embodiment is along the intake valve lift direction on the outer peripheral side of the intake valve valve seat 6a provided with the wall portion 10 on the intake introduction direction side. The wall portion 10a and the wall surface 10a of the wall portion 10 are smoothly continuous, and both are substantially a single wall surface.

  In such a fourth embodiment, when the first intake valve 21 is a minimal lift, the second wall portion 30 has a gap between the side wall 11a of the valve head 11 of the first intake valve 21 and the second wall portion 30. An intake flow flows in the direction of the piston along the wall surface 30a. At this time, since the clearance S between the wall portion 10 or the second wall portion 30 and the side surface 11a of the valve head 11 of the first intake valve 21 is larger than the lift amount of the first intake valve 21, the intake air flows into the wall portion 10. Or it is not restrict | limited by the 2nd wall part 30, and flows in into the combustion chamber 5 toward the piston direction from the perimeter of the 1st intake valve 21. FIG. Therefore, an unburned HC emission reduction effect can be obtained by making it possible to control the intake air amount by the lift amount during the minimum lift and reducing the amount of fuel adhering to the wall surface of the combustion chamber 5.

  Further, when the first intake valve 21 is in a small lift, the lift amount of the first intake valve 21 is larger than the clearance S between the side surface 11a of the valve head 11 of the first intake valve 21 and the wall portion 10, so that the first intake valve 21 Of the valve seat 6a for the intake valve on which the valve 21 is seated, the intake flow from the wall portion 10 on the intake introduction direction side decreases and the intake flow from the side opposite to the wall portion 10 (on the side opposite to the intake direction) increases.・ Tumble flow can be generated. At this time, since the height of the second wall portion 30 is smaller than the lift amount of the first intake valve 21, the second wall portion 30 has a small adverse effect on the occurrence of swirl and tumble flow.

  The technical ideas of the present invention that can be grasped from the above embodiments will be listed together with the effects thereof.

  (1) In an internal combustion engine in which the valve lift amount of the intake valve can be changed in accordance with the engine load, the intake wall is positioned on the upper wall surface of the combustion chamber that is in the vicinity of the valve seat of the intake valve and is relatively on the intake introduction direction side In a state where a wall portion is formed along the valve lift direction and the lift amount of the intake valve is a predetermined first lift amount, the clearance between the intake valve and the wall portion is larger than the first lift amount, and the intake valve is In a state where the lift amount is a second lift amount that is relatively larger than the predetermined first lift amount, the intake valve and the wall portion are arranged so that the second lift amount is larger than the clearance between the intake valve and the wall portion. Clearance is set. Thus, in a state where the lift amount of the intake valve becomes the first lift amount, the intake flow from the side where the wall portion around the valve seat of the intake valve is provided is increased, and the wall portion around the valve seat of the intake valve Reduces the intake air flow from the side where is not provided. In addition, in the state where the lift amount of the intake valve is the second lift amount, the intake flow from the side where the wall portion around the valve seat of the intake valve is provided is reduced, and the wall portion around the valve seat of the intake valve is reduced. The intake air flow from the side not provided increases. That is, in the state where the lift amount of the intake valve becomes the first lift amount, the fuel adhering to the wall surface of the combustion chamber is reduced by utilizing the rectification effect of the intake air flow by the wall portion, and the lift amount of the intake valve becomes the second lift amount. In this state, the intake flow from the side where the wall portion around the valve seat of the intake valve is not provided can be increased, and a high-speed directional intake flow can be generated.

  (2) In the internal combustion engine described in (1) above, the lift amount in the idle operation state is the first lift amount, and the lift amount in the low load operation state excluding the idle operation is the second lift amount. Thus, in the idle operation state, the fuel flow adherence to the wall of the combustion chamber is reduced by utilizing the rectification effect of the intake air flow by the wall portion. In the low load operation state except the idle operation, the wall around the valve seat of the intake valve It is possible to increase the intake air flow from the side where the portion is not provided and generate a high-speed directional intake air flow.

  (3) In the internal combustion engine according to (1) or (2), more specifically, two intake valves are provided per cylinder, and a wall portion is formed only for one intake valve. .

  (4) More specifically, in the internal combustion engine according to the above (3), the lift amount of the intake valve close to the wall portion is not at least smaller than the lift amount of the intake valve not close to the wall portion. Is set.

  (5) In the internal combustion engine according to the above (3) or (4), the upper wall surface of the combustion chamber that is in the vicinity of the valve seat of the intake valve close to the wall portion and relatively on the side opposite to the intake air introduction direction A second wall portion is formed along the intake valve lift direction.

Explanatory drawing which showed typically the combustion chamber shape of the internal combustion engine in 1st Embodiment of this invention. Sectional drawing in alignment with the AA of FIG. 1 at the time of an idle driving | running state after warming-up. Sectional drawing in alignment with the AA of FIG. 1 at the time of the low load driving | running state except idle operation after warming-up. Explanatory drawing which showed typically the combustion chamber shape of the internal combustion engine in 2nd Embodiment of this invention. Sectional drawing in alignment with the BB line of FIG. 4 at the time of idle operation state after warming-up. Sectional drawing along the BB line | wire of FIG. 4 at the time of the low load driving | running state except idle operation after warming-up. Sectional drawing along CC line of FIG. 4 at the time of an idle driving | running state after warming-up. Sectional drawing along CC line of FIG. 3 at the time of the low load driving | running state except idle driving after warming-up. Sectional drawing in alignment with the DD line | wire of FIG. 3 at the time of an idle driving | running state after warming-up. Sectional drawing along CC line of FIG. 4 which shows the case where the valve lift amount of a 2nd intake valve is made into the zero lift at the time of partial load. Explanatory drawing which showed typically the combustion chamber shape of the internal combustion engine in 3rd Embodiment of this invention. Sectional drawing along the EE line | wire of FIG. Explanatory drawing which showed typically the combustion chamber shape of the internal combustion engine in 4th Embodiment of this invention. Sectional drawing along the FF line of FIG. Sectional drawing along the FF line | wire of FIG. 13 at the time of an idle driving | running state after warming-up. Sectional drawing along the FF line | wire of FIG. 13 at the time of the low load driving | running state except idle operation after warming-up.

Explanation of symbols

2 ... Intake valve 5 ... Upper wall surface 6 ... Valve seat for intake valve 10 ... Wall

Claims (5)

In an internal combustion engine that can change the valve lift amount of the intake valve according to the engine load,
In the vicinity of the valve seat of the intake valve, a wall portion along the intake valve lift direction is formed on the upper wall surface of the combustion chamber that is relatively on the intake introduction direction side,
In a state where the lift amount of the intake valve becomes a predetermined first lift amount, the clearance between the intake valve and the wall portion is larger than the first lift amount, and the intake valve has a relative lift amount higher than the predetermined first lift amount. The internal combustion engine is characterized in that the clearance between the intake valve and the wall portion is set so that the second lift amount is larger than the clearance between the intake valve and the wall portion when the second lift amount is large. organ.   2. The internal combustion engine according to claim 1, wherein the lift amount in an idle operation state is a first lift amount, and the lift amount in a low-load operation state excluding idle operation is a second lift amount.   3. The internal combustion engine according to claim 1, wherein two intake valves are provided for each cylinder, and a wall portion is formed only for one of the intake valves.   The internal combustion engine according to claim 3, wherein the lift amount of the intake valve close to the wall portion is set so as not to be at least smaller than the lift amount of the intake valve not close to the wall portion.   A second wall portion is formed along the intake valve lift direction on the upper wall surface of the combustion chamber, which is in the vicinity of the valve seat of the intake valve close to the wall portion and relatively on the side opposite to the intake air introduction direction. The internal combustion engine according to claim 3 or 4, characterized by the above.

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