Internal-combustion engines – Starting device – Mechanical
Reexamination Certificate
2001-06-07
2004-11-02
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Starting device
Mechanical
C123S1960CP, C123S311000, C123S041560
Reexamination Certificate
active
06810849
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, generally, to four-stroke internal combustion engines and, more particularly, to four-stroke internal combustion engines used in trimmers, blowers, vacuums, chain saws, other hand-held power tools, snowblowers, generators, vegetation cutting devices such as lawn mowers, or other outdoor power equipment.
BACKGROUND OF THE INVENTION
Many hand-held power tools or other outdoor power equipment are powered by electric motors or two-stroke internal combustion engines. Electric motors are limited to certain applications due to the available power for products utilizing a cord, and battery longevity for cordless products. Conventional two-stroke engines include a lubricating means in which the lubricant is mixed with fuel which allows the engines to operate in any given position such as upright, inclined, sideways or upside down. For example, when using a chain saw, the chain saw is typically capable of use in either an upright, sideways or upside down condition. Over the past few years, there has been a requirement by various governing bodies to reduce the emissions associated with all small gas engines, particularly, conventional two-stroke engines. Thus, because four-stroke engines do not require the mixing of lubricant and fuel, it is desirable to use four-stroke engines in place of conventional two-stroke engines, since four-stroke engines normally release fewer undesirable emissions as compared to the amount of undesirable emissions released by conventional two-stroke engines.
However, previously, it was widely viewed that four-stroke internal combustion engines could only be used for limited applications, such as lawn mowers, snowblowers, generators, or other portable products having wheels. It was thought that these prior four-stroke engines were too heavy and cumbersome to be used in operator-carried power tools. Moreover, since it is generally necessary to store oil separate from the gas so that the oil can be used for lubrication, traditional low-cost four-stroke engines were not designed to operate in any position other than a substantially upright position because if the engine was significantly tipped or tilted, the lubricant would foul the engine. Only very recently has it been contemplated that a four-stroke engine may be used in a hand-held power tool or in other applications where the engine may operate in a tipped or tilted condition.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a four-stroke internal combustion engine that is capable of use in various power tools, and yet is also capable of having low emissions and being sufficiently light to be carried by an operator when desired. What is also needed is a four-stroke internal combustion engine that is capable of operating in many different attitudes of the engine. What is also needed is a four-stroke engine that eliminates the need for an elaborate lubrication system. What is needed is a four-stroke internal combustion engine which accomplishes these features and other features and which is also economical to manufacture.
In one embodiment of the present invention, there is provided a four-stroke internal combustion engine, preferably a side valve or “L” head engine, having an engine housing which includes a crankcase and a cylinder. A cylinder head which at least partially defines a combustion chamber is positioned adjacent to the cylinder. An intake valve and an exhaust valve are disposed within the engine housing. A crank chamber and an oil reservoir are disposed within the crankcase in such a way that the oil reservoir is in fluid flow communication with the crank chamber. A strategically placed agitator, located at least partially within the crank chamber, moves lubricant within the engine housing during operation of the engine to lubricate the necessary components of the engine.
A divider is disposed within the crankcase to at least partially divide the crank chamber and the oil reservoir. The divider assists in directing the lubricant during operation and storage of the engine in order to prevent a substantial amount of lubricant from undesirably migrating into the combustion chamber when the engine is operated or stored in an upright or tilted position. In one aspect of the present invention, the divider defines a path which extends about the divider. The path allows lubricant in the oil reservoir to flow around a substantial portion of the divider to further enhance the lubricating and storage features of the engine according to the principles of the present invention.
The engine is constructed of light weight material and appropriately sized so that the engine is sufficiently light enough to be usable in hand-held power tools. Thus, the four-stroke internal combustion engine according to the present invention may be utilized in those applications which are traditionally limited to the use of two-stroke internal combustion engines.
In one aspect of the present invention, the divider includes at least one opening such that the crank chamber and the oil reservoir are in fluid flow communication through the opening. The opening helps ensure that the crank chamber is substantially continuously lubricated during operation of the engine, even if the engine is operated under a tilted condition. The opening in the divider is positioned such that at least some of the lubricant found in the crank chamber after operation of the engine may flow back into the oil reservoir even if the engine is stored in a tilted state. Preferably, the divider includes a plurality of openings.
In another aspect of the present invention, the engine housing further includes a cylinder side wall which at least partially extends into the crank chamber to define a lubricant receiving space between the divider and the cylinder side wall. Preferably, the cylinder side wall at least partially defines a piston bore. During operation, as the agitator mixes and slings lubricant around the inside cavity of the engine as a result of the rotating action of the agitator, the lubricant is more likely to be slung into the open area between the divider and the cylinder side wall rather than into the piston bore. Moreover, during storage, the open area or lubricant receiving space provides additional space for the lubricant to be held if the engine is stored in a sideways or upside down position to also prevent a substantial amount of the lubricant from flowing into the piston bore. As previously noted, migration of the lubricant into the combustion chamber leads to an unwanted condition. A function of the lubricant receiving space is to inhibit lubricant from reaching the piston bore, thereby preventing a substantial amount of lubricant from reaching the combustion chamber.
In another aspect of the present invention, the engine housing further includes a valve chamber. The intake valve and exhaust valve are disposed within the valve chamber and the valve chamber is in fluid flow communication with the crank chamber. The operation of the agitator, the pressure pulses created within the engine during operation of the engine, the communication of the oil reservoir with the crank chamber, and the communication of the crank chamber with the valve chamber together allow the working components found within the valve chamber to be lubricated, even if the engine is operated in a tilted manner. Preferably, the valve chamber is also in fluid flow communication with the cylinder side wall to further enhance the lubrication of the working components located within the valve chamber. The strategic positioning of the fluid flow openings into the valve chamber will prevent the valve chamber from receiving too large of a quantity of lubricant when the engine is being operated or being stored.
In another embodiment of the present invention, the engine includes a cantilevered crankshaft which has opposite ends and which is substantially located within the crank chamber. The agitator includes a counterweight which is interconnected to the cantilevered end of the crankshaft. The counterweight is adapted to
Bartelt Ronald Lee
Braun Michael Paul
Hirsch Nicholas Robert
Hotz Peter
Hubbard Brian
Argenbright Tony M.
Briggs & Stratton Corporation
Harris Katrina B.
Michael & Best & Friedrich LLP
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