BACKGROUND OF THE INVENTION

This invention relates to cylinders for two-cycle internal combustion engines and more particularly, to unique design of exhaust port for reducing the distortion of cylinders during operation.

BACKGROUND

The problems and disadvantages of two-cycle internal combustion engines are known. Generally, a two-cycle internal combustion engine includes a cylinder defined by a cylinder wall. A cylinder bore is disposed within cylinder and is adapted to receive a reciprocating piston. The piston reciprocates along a longitudinal axis of cylinder bore.
Projecting outwardly from cylinder is a plurality of spaced fins or air vanes that assist in heat dissipation from the air-cooled engine.

Generally, the cylinders have at least an exhaust and an intake port that are open or closed by the reciprocating movement of the piston. During exhaust the temperature near the exhaust port becomes very high compared to the other parts of the cylinder as hot exhaust gases passes through the exhaust port transferring substantial amount of heat to the sections that are in near vicinity of the exhaust port by means of conduction. Thus resulting in irregular distribution of heat that causes irregular thermal expansion, and consequently distortion of cylinder bore.

One major disadvantage of the cylinder bore distortion is that exhaust emissions are increased. Since the piston and rings have a substantially circular shape in cross section and the bore has a non-circular shape in cross section during engine operation due to bore distortion, it is apparent that small gaps will exist between the piston and ring outer wall surface and the bore inner surface. These gaps permit oil and gasses from the crankcase to leak into the combustion chamber and eventually out the exhaust valve into the environment. Exhaust emissions are thus undesirably increased due to the cylinder bore distortion. Further, the life and durability of piston and engine considerably decreases.
One prior art way to substantially eliminate the cylinder bore distortion has been to uniformly and substantially increase the thickness of cylinder wall along the entire length and the entire circumference of the cylinder. Although this method is effective, it greatly increases the amount of material that must be used in forming the engine housing.
Particularly when the engine housings are mass-produced in many thousands or even millions of units, the additional cost of providing such cylinder wall reinforcement is quite substantial. Another way to reduce cylinder bore distortion is to provide typically asymmetrical distribution of air vane having a much greater size and density at section near the exhaust port. However, this is limited by the space limitation owing to the design of cylinder.

SUMMARY OF THE INVENTION

Accordingly, a two-cycle internal combustion engine is disclosed having a cylinder block, means defining a cylinder bore in the cylinder block and a means defining an exhaust port through the cylinder block along an exhaust port axis from the cylinder bore to an outside of the engine block. In a preferred embodiment, the peripheral boundary of the exhaust port that defines an exhaust passage from the cylinder bore to the outside of the cylinder block along said exhaust port axis, is formed of a dual wall having two walls spaced from each other throughout the length of said axis and joined together at ends enclosing the air in the space between the said two walls. Thus, air enclosed in the space between the walls acts as heat insulation and consequentially the heat transfer from the exhaust gases to the section surrounding the exhaust port is greatly reduced. This minimizes the irregularity in distribution of heat to such levels that the possibility of cylinder bore distortion greatly reduces.

Other advantages and features of the invention will become apparent from the following description including the drawings and claims. The above-explained preferred embodiments are exemplary of the invention of the present application. It should be understood that modifications of the preferred embodiments might be made as would occur to one skilled in the art.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 depicts a two-wheeled vehicle having a two-cycle engine.

Figure 2 depicts cross-section view of cylinder block of a two-cycle engine
embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to drawings, a two-wheeled vehicle 01 having a two-cycle internal combustion engine is depicted. The said engine having a combustion chamber defined by cylinder head 02, a cylinder bore 05 having facing distally opposite intake port 09 and exhaust port 06 defined by the cylinder block 04.

A piston axially reciprocable in the cylinder bore 05. The piston moves upwardly in a charging stroke, and downwardly in a power stroke. The piston is rotatably journaled to the upper end of a connecting rod that has a lower end rotatably journaled to a crankshaft, all as is known in the art. During the upward charging stroke of piston, a vacuum is created in crankcase 03 which draws a fuel-air mixture through the induction system.
During the downward power stroke of piston, crankcase is pressurized, which forces the fuel-air mixture in crankcase to flow through transfer passage to intake port 09 to introduce the fuel-air charge into combustion chamber. Upon the upward stroke of piston, the fuel-air mixture in combustion chamber is compressed for ignition by spark plug, and the spent combustion products are exhausted at exhaust port 06 during the downward power stroke of the piston. In the present embodiment exhaust port 06 extends through the cylinder block 04 along an exhaust port axis from the cylinder bore 05 to an outside of the cylinder block 04, the inner peripheral boundary of the exhaust port 06 that defines an exhaust passage from the cylinder bore 05 to the outside of the cylinder block 04 along said exhaust port axis, is formed of a dual wall having two walls 07 and 07A spaced from each other throughout the length of said axis and joined together at ends, enclosing air in the space 08 between the said two walls. Thus, air enclosed in the space 08 between the walls acts as heat insulator and consequentially the heat transfer from the exhaust gases to the section of the cylinder block in the close vicinity the exhaust port is greatly reduced.
This minimizes the irregularity in distribution of heat to such levels that the possibility of cylinder bore distortion greatly reduces.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the claims.

We Claim:

1. A two-cycle internal combustion engine comprising:

a cylinder block;

a means defining a cylinder bore in the cylinder block;

a piston reciprocable therein; and

a means defining an exhaust port through the cylinder block along an exhaust port axis from the cylinder bore to an outside of the cylinder block;

said cylinder block being opened and closed by reciprocating motion of the piston in the cylinder to control the passage of exhaust gas from the cylinder through an exhaust passage defined by inner peripheral boundary of the exhaust port, from the cylinder bore to the outside of the cylinder block along said exhaust port axis wherein, said inner peripheral boundary is formed of two walls spaced from each other throughout the length of said axis and joined together at ends defining a space enclosing air, between the said walls;

2. The two-cycle internal combustion engine as claimed in claim 1,

wherein the said two walls formed in exhaust port encloses the air in the space between the walls and thereby acts as heat insulator.