Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2000-05-18
2001-11-20
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0650PD, C123S193600
Reexamination Certificate
active
06318311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cylinder-injection type two cycle combustion engine where fuel is directly injected into a combustion chamber.
2. Description of the Related Art
A conventional cylinder-injection type two cycle combustion engine is provided with a cylinder, a piston reciprocating within the cylinder, a fuel injector for directly injecting fuel into a combustion chamber, a spark plug for igniting mixture of fuel injected into the combustion chamber and air, an exhaust port provided at the cylinder so as to perform exhaust when the piston is moved downward, a plurality of scavenging paths provided along a circumferential direction in a spaced manner for scavenging the combustion chamber when the piston is moved downward, and a crank shaft which is transmitted with upward and downward movements of the piston to be rotated. In this case, the cylinder is formed with a cylinder body formed in a cylindrical shape with its proximal end opened towards a crank chamber, a liner provided in a cylindrical manner so as to cover an inner surface of the cylinder body, and a cylinder head closing a distal end opening of such a cylinder body. The fuel injector and the spark plug are assembled to the cylinder head. The fuel injector is structured so as to directly inject fuel towards a head portion of the piston. A recessed portion is provided at a position on a head portion of the piston against which fuel from the fuel injector directly strikes or in the vicinity thereof, so that the fuel injected from the fuel injector is reflected at the recessed portion towards an inner surface of the cylinder head. The respective scavenging paths are provided along and between the cylinder body and the liner positioned on an inner surface thereof, and their outlet ports are opened to the liner. Inlet ports of the scavenging paths are respectively opened to the crank chamber. Incidentally, there is a case where a liner is not provided on an inner surface of a cylinder body. In such a case, respective scavenging paths are formed in the block of the cylinder body along the axial direction thereof.
In such a conventional cylinder-injection type two cycle combustion engine, the top portion of the piston is formed in a generally horizontal surface or flat surface so as to facilitate injection of scavenging air from the respective scavenging paths into the cylinder at a scavenging time.
In such a conventional cylinder-injection type two cycle combustion engine, however, since the top portion of the piston is made generally flat except for the recessed portion, scavenging air merely flows along the top portion, so that cooling for the piston becomes insufficient at a scavenging time. As a result, there has been a drawback that the temperature of the top portion of the piston becomes high, and in some cases, the piston seizes the liner or the inner surface of the cylinder.
In order to prevent the piston from seizing, there is a method where a clearance between the liner or the inner surface of the cylinder body and the outer peripheral surface of the piston is secured excessively. In such a case, however, there has been a drawback that such a demerit as reduction in engine output or power, increase in piston striking noises or the like is caused.
An object of the present invention is to provide a cylinder-injection type two cycle combustion engine where seizure of a piston can be prevented without excessively forming a clearance between a liner or an inner surface of a cylinder and an outer surface of a piston.
Another object of the invention is to provide a cylinder-injection type two cycle combustion engine where cooling a piston can efficiently be performed at least in the vicinity of an exhaust port in which seizure of a piston is easy to occur.
SUMMARY OF THE INVENTION
The present invention is applied to a cylinder-injection type two cycle combustion engine provided with a cylinder, a piston reciprocating within the cylinder, a fuel injector for directly injecting fuel into a combustion chamber and a spark plug for igniting mixture of fuel injected into the combustion chamber and air, an exhaust port provided at the cylinder so as to perform exhausting when the piston is moved downward, and a plurality of scavenging paths for performing scavenging of the combustion chamber when the piston is moved downward.
In the present invention, a top portion of the piston has a convex portion with an inclination surface of which inclination extends in a direction of the top portion of the cylinder from an outer periphery of the piston towards a central portion side. The inclination surface of the convex portion is formed such that scavenging air from at least a scavenging path near to the exhaust port is blown directly on to the inclination surface.
When the convex portion is provided at the top portion of the piston so that scavenging air is directly blown on the inclination surface positioned about the top of the convex portion, the top portion of the piston is efficiently cooled with scavenging air and the piston is prevented from seizing due to excessive thermal expansion.
In the present invention, it is preferable that the inclination surface of the convex portion on the top portion of the piston is configured in the following manner according to whether the contour of a vertical section thereof is formed in a linear inclination surface or it is formed in a curved inclination surface.
In the case that the inclination surface of the convex portion on the top portion of the piston is formed in the linear inclination surface, an angle &thgr; between a ceiling surface at an outlet port of at least a scavenging path of the scavenging paths which is near to the exhaust port and a perpendicularly crossing surface perpendicularly crossing the axial line of the cylinder is made smaller than an angle &agr; between the linear inclination surface and a perpendicularly crossing surface perpendicularly crossing the axial line of the piston.
When the inclination surface of the convex portion on the top portion of the piston is formed in the curved inclination surface, the angle &thgr; between a ceiling surface at an outlet port of at least a scavenging path of the scavenging paths which is near to the exhaust port and a perpendicularly crossing surface perpendicularly crossing the axial line of the cylinder is made smaller than an angle &bgr; between a tangential line extending from the outer periphery of the top portion of the piston toward the center of the top portion regarding the curved inclination surface and a perpendicularly crossing surface perpendicularly crossing the axial line of the piston.
Thus, when the angle &thgr; between a ceiling surface at an outlet port of at least a scavenging path near to the exhaust port and a perpendicularly crossing surface perpendicularly crossing the axial line of the cylinder is set in this manner, scavenging air from at least a scavenging path near to the exhaust port can securely be blown on the inclination surface of the top portion of the piston.
When the recessed portion is provided at the top portion of the piston in the above manner, there occurs a drawback that an amount of scavenging air required for the combustion chamber may not be obtained due to increase in resistance at a scavenging time. Such a drawback can be solved by enlarging a cross-sectional area of an opening of the scavenging path.
In the present invention, the top portion of the piston denotes a distal end or upper end of the piston facing the combustion chamber.
Also, in the cylinder-injection type two cycle combustion engine of the present invention, an upper portion denotes a cylinder head side or a top portion side of the piston, and a lower portion denotes a side opposed thereto. However, even when the cylinder-injection type two cycle combustion engine is arranged in a horizontal or transverse manner, the upper portion and the lower portion are called in the same manner as the above in this invention.
REFERENCES:
patent: 4056080 (197
McMahon Marguerite
Pearne & Gordon LLP
Tohatsu Corporation
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