Intake system of an internal combustion engine

#The present invention relates to an intake system of an internal combustion engine.

#Particularly in a compression-ignition type internal combistion engine, in order to create a strong swirl motion in the combustion chamber of an engine at the time of the intake stroke, a helically-shaped intake port comprising a substantially straight inlet passage portion and a helical portion is used. However, even if such a helically-shaped intake port is applied to a spark-ignition type gasoline engine and, in addition, a slight change of the construction of the helically-shaped intake port is effected so as to create a swirl motion of the strength necessary to obtain a good combustion when the engine is operating under a light load, since the engine speed normally used in a gasoline engine is considerably greater than that normally used in a compression-ignition type engine, the flow resistance to which the mixture flowing in the helically-shaped intake port is subjected becomes large in a gasoline engine. As a result, the volumetric efficiency is reduced when the gasoline engine is operating at a high speed under a heavy load.

#In addition, particularly in a multi-cylinder internal combustion engine, there is a problem in that a uniform swirl motion cannot be created in each cylinder, even if each of the intake ports is merely shaped in the form of a helically-shaped intake port.

#In the drawings:

#FIG. 1 is a plan view of an internal combustion engine according to the present invention;

#FIG. 2 is a cross-sectional side view taken along the line II--II in FIG. 1;

#Referring to FIGS. 1 and 2, a cylinder block 1 has a piston 2 movable reciprocally therein. A cylinder head 3 is fixed onto the cylinder block 1 and a combustion chamber 4 is formed between the piston 2 and the cylinder head 3. An intake valve 5 is located in a helically-shaped intake port 6 formed in the cylinder head, an exhaust valve 7 is located in an exhaust port 8, and a spark plug 9 is located in the head 3 between the valves 5 and 7. An intake manifold 10, on which a carburetor 11 is mounted, has manifold branches 12 attached to the cylinder head. Each of the manifold branches 12 is connected to the corresponding intake port 6. As is illustrated in FIG. 2, a cylindrical projection 14, projecting downwardly for supporting a valve guide 13, is formed in one piece on the upper inner wall of the helically-shaped intake port 6, and the tip of the valve guide 13 projects from the tip of the cylindrical projection 14. At the time of the intake stroke, the mixture formed in the carburetor 11 (FIG. 1) is introduced into the combustion chambers 4 via the intake manifold 10, the manifold branches 12, the helically-shaped intake ports 6 and the intake valves 5 and is ignited by the spark plug 9 at the end of the compression stroke.

#FIGS. 4 through 7 schematically illustrate the shape of the helically-shaped intake port 6 illustrated in FIG. 2. As is illustrated in FIG. 5, the helically-shaped intake port 6 comprises an inlet passage portion A extending substantially straight along the longitudinal central axis a thereof, and a helical portion B. The open inlet end of the inlet passage portion A has a rectangular cross-section (FIG. 8), and the mixture outlet portion 15 (FIG. 4) of the helical portion B has a cylindrical inner wall which extends circumferentially about the helix axis b of the helical portion B. As illustrated in FIG. 2, the helix axis b, that is, the axis of the intake valve 5, is inclined by approximately 23 degrees with respect to the axis of the cylinder, and the inlet passage portion A extends substantially horizontally. The side wall 16 of the inlet passage portion A, which is located remote from the helix axis b, is arranged so as to be substantially vertical and is smoothly connected to the side wall 17 of the helical portion B, which extends circumferentially about the helix axis b. As illustrated in FIGS. 7 and 10, the side wall 17 of the helical portion B is so formed that it expands outwards from the cylindrical inner wall of the mixture outlet portion 15. In addition, as is illustrated in FIG. 5, the side wall 17 is so formed that the distance R between the side wall 17 and the helix axis b is maintained constant at a position near the inlet passage portion A and is gradually reduced along the helical direction C. The distance R becomes approximately equal to the radius of the cylindrical inner wall of the mixture outlet portion 15 (FIG. 4) at the helix terminating portion E.

#As is illustrated in FIGS. 4 and 5, the side wall 18 of the inlet passage portion A, which is located near the helix axis b, has on its upper portion an inclined wall portion 18a which is arranged to be directed downwards. The width of the inclined wall portion 18a is gradually increased towards the helical portion B and, as is illustrated in FIGS. 5 and 9, the entire portion of the side wall 18 is inclined at the connecting portion of the inlet passage portion A and the helical portion B. The upper half of the side wall 18 is smoothly connected to the circumferential wall of the cylindrical projection 14 (FIG. 2), and the lower half of the side wall 18 is connected to the side wall 17 of the helical portion B at the helix terminating portion E of the helical portion B.