Internal combustion engine

Details Internal combustion engine Internal combustion engine

1999-06-21

2000-11-28

McMahon, Marguerite

Internal-combustion engines

Two-cycle

Whirl through piston-controlled ports

123 65EM, 123 65PE, F02B 3304

Patent

active

061520926

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The subject invention refers to a crankcase scavenged internal combustion engine of two-stroke type, intended for a working tool, preferably a chain saw or a trimmer, and provided with a light-weight and compact muffler.


BACKGROUND OF THE INVENTION

For working tools run by internal combustion engines generally two-stroke engines are used, mainly due to their low weight and simple design. Also, the crankcase scavenging enables a lubrication system independent of position, in which the engine is lubricated by oil which is added to the air-fuel mixture scavenged through the crankcase. The all-position lubrication system is necessary e.g. for chain saws since they are to be used in a lot of different working positions. Two-stroke engines for mopeds and motor-cycles generally have a so called tuned exhaust system. Reflecting pressure pulses from the exhaust system will press scavenging gases back into the cylinder so that the engine's scavenging losses are reduced. In total this means that both the power output and fuel consumption can be improved in comparison with a non-tuned exhaust system. However, in order to function the tuning requires very large lengthes of pipe in the exhaust duct. Such a muffler for a chain saw would be at least half a meter long and consist of a first conically expanding duct section by approximately 8 degrees, and a second conically narrowing section by approximately 12 degrees. Thereafter an absorption muffler should be connected in order to reach reasonable sound-levels. As mentioned above such a muffler is built on reflecting pressure pulses as well as a low total fall of pressure. Regarding working tools it has turned out that such a muffler will be far too large and heavy. This even if the pipe system is provided with a lot of curves. For, a working tool must be very light-weight, compact and handy in order to serve its purpose. Consequently, tuned exhaust systems are normally not used for working tools. Instead they have light-weight and compact mufflers in which the sound mainly is damped by throttling in the muffler. A larger cylinder volume is used to reach the preferable effect. Owing to the fact that there are great differences between the lay out of two-stroke engines with tuned exhaust systems and without tuned exhaust systems, it is difficult to transfer experiences from one area to another.
A well-known problem with two-stroke engines is their relatively high fuel consumption caused by high scavenging losses, i.e. scavenging gases which go straight out into the exhaust system. This also results in high emissions, especially from hyrdocarbons. As mentioned above, the difficulties to overcome this problem are especially big for two-stroke engines with light-weight and compact mufflers, i.e. with non-tuned exhaust systems. The high extent of emissions from hydrocarbons also results in certain problems when using a muffler with catalytic conversion. For, the very high energy of the exhaust gases leads to a very high heat generation in the catalytic converter as well as in the surrounding muffler. This high extent of heat generation could mean that the conversion ratio in the catalytic converter must be kept down. Consequently, the high scavenging losses would increase the fuel consumption at the same time as they could complicate a cooperation with an exhaust catalytic converter.


PURPOSE OF THE INVENTION

The purpose of the subject invention is to substantially reduce the above outlined problems for a crankcase scavenged internal combustion engine of two-stroke type, provided with a light-weight and compact muffler.


SUMMARY OF THE INVENTION

The above mentioned purpose is achieved in an arrangement, in accordance with the invention, having the characteristics appearing from the appended claims.
The crankcase scavenged internal combustion engine in accordance with the invention is thus essentially characterized in that the engine is arranged with a particularly high crankcase compression created in that at least one filling is placed in the compress

REFERENCES:
patent: 941376 (1909-11-01), Lucas
patent: 2246446 (1941-06-01), Kylen
patent: 4682571 (1987-07-01), Kaufman et al.
patent: 4934345 (1990-06-01), Fukuoka et al.
patent: 5794605 (1998-08-01), Kato

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