Exhaust port of two cycle engine
AssigneeTextron Inc.
InventorMervyn B. Johnston
Life of this patent
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Abstract
The exhaust port of a spark ignition two cycle engine has the general shape of an inverted T with a base portion and a narrower upwardly extending stem portion. The top of the base portion is approximately at the level of the top of the transfer port which admits fuel-air mixture to the engine cylinder. The top of the stem is from 20.degree. to 55.degree. of crankshaft rotation in advance of the opening of the transfer port. This configuration of the exhaust port produces a low broad blowdown pulse which in turn results in a low noise level of the exhaust.
Claims8
In a spark ignition two cycle internal combustion engine comprising a cylinder having a head, a crankshaft and a piston connected to said crankshaft and reciprocable in said cylinder, said cylinder having a single exhaust port and a transfer port successively uncovered by said piston to exhaust burned gasses from said cylinder and to admit a fresh charge of fuel-air mixture to said cylinder, the improvement that the exhaust port has the general shape of an inverted T with a wider base portion and a narrower stem portion extending upwardly toward the head of said cylinder, the bottom of said base portion being at bottom dead center of piston reciprocation, the top of said base portion being approximately at the level of the top of said transfer port and the top of said stem portion being from 20.degree. to 55.degree. in advance of the top of said transfer port, said stem portion comprising an upper section and a lower section of greater length than said upper section, the width of said exhaust port being approximately uniform throughout the length of said lower stem section to provide selected blowdown before the transfer port is opened and the width increasing abruptly at said base portion at approximately the level of the top of said transfer port to effect rapid lowering of cylinder pressure, the values of the width x of said upper section of the stem portion and width y of said lower section both expressed as percentages of the internal diameter of the cylinder, and the values of the length a of said upper section, the length b of said lower section and the lead L of the exhaust port opening over transfer port opening, all three expressed in degrees of crank shaft rotation being within the following ranges:
- a = 0.degree. - 15.degree.
- b = 10.degree. - 55.degree.
- x = 5 - 35 percent
- y = 5 - 30 percent
- L = 20.degree. - 55.degree.
- and satisfying the following relationship:
- 800 .ltoreq. a.sup.. x.sup.1.3 + b.sup.. y + 20(L-20).ltoreq. 1200,
- whereby the engine when running produces a low broad blowdown pulse which in turn produces a low noise level exhaust.
Dependencies are inferred from the claim text.