Drive unit

Details Drive unit Drive unit

1999-03-15

2001-04-10

Kamen, Noah P. (Department: 3747)

Internal-combustion engines

Two-cycle

Rear compression

C123S184230, C123S543000

Reexamination Certificate

active

06213066

ABSTRACT:

TECHNICAL FIELD
The subject invention refers to a drive unit for a handheld working tool, such as a chainsaw, trimmer or hedge trimmer, said drive unit essentially comprises a housing part with a fuel tank and an engine unit with a fuel supply unit, such as a carburetor, a muffler and a crankcase scavenged combustion engine, with cylinder, piston and crankshaft.
BACKGROUND OF THE INVENTION
Due to requirements of low weight and compact design portable working tools are usually run by a crankcase scavenged two-stroke engine. However, a crankcase scavenged four-stroke engine is also conceivable. As a result of the crankcase scavenging, oil mixed with the fuel lubricates the engine. This means that the tool can be oriented in different directions while running, such as sideways or upside-down. The tools usually have a carburetor connected to an inlet duct, but also a low pressure injection system can be of interest. Since the tool can be used in a lot of positions there is a risk for fuel drops to accumulate inside the inlet duct and then be tipped into the cylinder when the tool's inclination is changed. This can bring about that the engine stops. The greatest risk for this is at lower engine speed. For this reason, the carburetor is usually placed near the inlet port resulting in a short inlet duct. Considering engine power at operating speed it would however be preferable to use a longer inlet duct. This could however be associated with said difficulties as well as pure space problems. Therefore the carburetor is usually adjacent the cylinder's top section, and provided With some kind of heat protecting baffle. This baffle implies a complication at the same time as temperature problems can still arise for the carburetor. Furthermore, the inlet duct usually turns obliquely downward towards the crankcase. Owing to this the inlet gases can not assist in cooling the critical area around the exhaust port.
PURPOSE OF THE INVENTION
The purpose of the subject invention is to substantially reduce the above outlined problems.
SUMMARY OF THE INVENTION
The above mentioned purpose is achieved in a drive unit, in accordance with the invention, having the characteristics appearing from the appended claims.
The drive unit according to, the invention is thus essentially characterized in that at least one inlet port is located in the engine cylinder wall and/or in an adjacent part of the engine crankcase, arid that the engine inlet duct from the inlet port up to the fuel supply unit has a length longer than 1.8 times the engine cylinder stroke, preferably longer than 2.0 times the cylinder stroke. The long inlet duct gives advantages but also implies a number of risks as mentioned above. It requires an elaborate drawing of the inlet duct so that the risk for fuel drops to accumulate in the inlet duct is reduced. Furthermore it is advantageous to have a long preheated section of the inlet duct, which vaporizes fuel drops and thus reduces said risks. By a suitable angling of the inlet duct a cooling effect can also be created around the cylinder's exhaust port and adjacent parts of the piston. These and other characteristic features and advantages of the invention will become apparent from the following detailed description of various embodiments with the support of the annexed drawing.


REFERENCES:
patent: 4607598 (1986-08-01), Kamata
patent: 5699761 (1997-12-01), Yamaguchi et al.
patent: 70531 (1983-04-01), None
patent: 3916414 (1991-01-01), None
patent: 2911497 (1991-02-01), None

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