Internal-combustion engines – Particular piston and enclosing cylinder construction – Cylinder head
Reexamination Certificate
1999-11-24
2001-04-03
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Cylinder head
Reexamination Certificate
active
06209505
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four-cycle engine for a vehicle, in which a cylinder bore is disposed in such a manner that the axial line of the cylinder bore extends substantially in the horizontal direction. Furthermore, a cam shaft is disposed between an intake valve and an exhaust valve which have operational axial lines crossing each other, forming an approximately V-shape.
2. Background Art
In a prior art four-cycle engine including an intake valve and an exhaust valve having operational axial lines crossing each other in an approximately V-shape, a diameter of the intake valve is larger than that of the exhaust valve. Accordingly, in order to make the squish area of the combustion chamber on the intake side and that on the exhaust side equal to each other, as disclosed in Japanese Patent Publication No. Hei 1-14406, an angle formed between the operational axial line of an exhaust valve and the axial line of the cylinder bore is set to be larger than an angle formed between the operational axial line of the intake valve and the axial line of the cylinder bore.
In the four-cycle engine for a vehicle in which the axial line of the cylinder bore extends substantially in the horizontal direction and the intake valve and the exhaust valve are disposed on the upper and lower sides of the cylinder head respectively, since a distance between the axial line of the cylinder bore and the outer end portion of the exhaust valve becomes large, both the cylinder head and the head cover protrude substantially downwardly. This results in the height of the engine from the road surface on which the vehicle is grounded not being able to be reduced. In particular, for a four-cycle engine mounted on a motorcycle of a type in which the axial line of a cylinder bore extends in the width direction of the motorcycle, since the position of the outer end portion of the exhaust valve exerts a large effect on the bank angle of the motorcycle, the mounting position of the engine to the body frame must be made relatively high.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide a four-cycle engine for a vehicle, which is capable of making the position of the outer end portion of an exhaust valve as close to the axial line of a cylinder bore as possible, thereby making the mounting position of the engine as low as possible.
To achieve the above object, according to a first aspect of the present invention, there is provided a four-cycle engine for a vehicle, in which a cylinder head is connected to a cylinder block including a cylinder bore having an axial line extending substantially in the horizontal direction in such a manner that a combustion chamber is formed between the cylinder head and a piston slidably fitted in the cylinder bore. An intake valve for taking air in the combustion chamber is openably/closably supported at an upper portion of the cylinder head. An exhaust valve for discharging exhaust gas from the combustion chamber is openably/closably supported at a lower portion of the cylinder head. Operational axial lines of the intake valve and the exhaust valve cross each other including the axial line of the cylinder bore, forming an approximately V-shape on a projection plane perpendicular to the axial line of a crank shaft. Furthermore, a cam shaft common to the intake valve and the exhaust valve has an axial line parallel to the crank shaft and is disposed between the intake valve and the exhaust valve. The four-cycle engine includes a cam shaft disposed above the axial line of the cylinder bore, and on the projection plane, an angle formed between the axial line of the cylinder bore and the operational axial line of the intake valve is set to be larger than an angle formed between the axial line of the cylinder bore and the operational axial line of the exhaust valve.
With this configuration, since the cam shaft is disposed above the axial line of the cylinder bore, and an angle formed between the operational axial line of the exhaust valve and the axial line of the cylinder bore is set to be smaller than the angle formed between the operational axial line of the intake valve and the axial line of the cylinder bore, it is possible to make the outer end portion of the exhaust valve as close to the axial line of the cylinder bore as possible, and hence to make the mounting position of the engine as low as possible while ensuring sufficient ground clearance. This makes it possible to lower the center of gravity of the vehicle and hence to improve the steering of the vehicle.
According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, on the projection plane, a crossing point of the operational axial lines of the intake valve and the exhaust valve is disposed under the axial line of the cylinder bore. With this configuration, it is possible to easily ensure a squish area on the side of the intake valve having a diameter larger than that of the exhaust valve, and hence to make the squish area on the intake valve side nearly equal to that on the exhaust side.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4267811 (1981-05-01), Springer
patent: 4505236 (1985-03-01), Nakamura
patent: 5228419 (1993-07-01), Nonogawa
patent: 5230317 (1993-07-01), Nonogawa et al.
patent: 5363818 (1994-11-01), Iwata et al.
patent: B2-114406 (1989-03-01), None
Hori Yoshiaki
Nishi Tohru
Honda Giken Kogyo Kabushiki Kaisha
McMahon Marguerite
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