Internal-combustion engines – Valve – Reciprocating valve
Reexamination Certificate
1999-02-17
2001-03-20
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Valve
Reciprocating valve
C123S188600
Reexamination Certificate
active
06202616
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a valve seal assembly, and more particularly to a valve seal assembly for preventing a lubricating fluid from entering the combustion chamber of an internal combustion engine.
BACKGROUND PRIOR ART
In many countries, governments are requiring manufacturers to reduce the amount of emissions which are expelled from small internal combustion engines. Manufacturers of internal combustion engines are therefore constantly developing new ways to reduce emission levels.
One source of unwanted emissions develops when the fluids, (typically conventional motor oil), that are used to lubricate the valve stems and valve guides within an internal combustion engine escape from the engine. In many engines, the lubricating fluid escapes past the valve seals, through the intake and the exhaust valve guides, and thereafter enters the intake and exhaust manifolds through the valve ports.
The level of unwanted exhaust emissions increases when the lubricating fluid escapes from the exhaust valve guide because the lubricating fluid is then expelled from the engine along with the rest of the emissions. The level of unwanted emissions also increases when the lubricating fluid escapes past the intake valve guide. The lubricating fluid that escapes past the intake valve guide enters the combustion chamber. Since the lubricating fluid is not readily combustible under these conditions it is not completely burned, and as a result the lubricating fluid is expelled from the engine as emissions. Carbon deposits are also formed on and around the intake valve head in addition to the inner surfaces of the internal combustion chamber. These deposits absorb some of the hydrocarbons contained within the air/fuel mixture that is input into the combustion chamber. The hydrocarbons are absorbed into the deposits during the compression stroke of the engine, causing the absorbed hydrocarbons to escape combustion. The absorbed hydrocarbons are then released during the exhaust stroke, resulting in increased levels of unwanted emissions.
Valve seal assemblies are commonly installed on the cylinder head in an engine having an overhead-valve configuration, and in the engine block on an engine having a side valve configuration. The valve seal assemblies are usually located on the end of the valve guide that is farthest from the combustion chamber. Conventional valve seal assemblies also include a resilient seal element that is compressed against the valve stem in order to prevent most of the lubricating fluid from travelling past the sealing element.
Valve seal assemblies are commonly installed over protruding portions of valve guide inserts. Conventional valve seal assemblies are also inserted into counterbores. The valve seal assemblies typically include a bottom surface that is sealingly engaged with the bottom surface of the counterbore. The bottom surface of the counterbore does not provide a sufficiently smooth finish capable of satisfactorily sealing the valve seal assembly with the counterbore due to the presence of jagged cutters on the cutting tool used to create the bottom surface of the counterbore.
One drawback associated with using known valve seal assemblies is the design of the lips in the sealing elements. Conventional lip designs typically allow some lubricant to leak past because the seal assembly is located on the end of the valve guide which is farthest from the combustion chamber. The valve seal assembly must allow some amount of lubricant to leak past the sealing element or the valve stem and valve guide will not receive any lubricant. Once the lubricant enters the valve guide it can travel along the length of the valve stem and valve guide until it enters the valve port. As stated previously, when the lubricating fluid passes through the valve ports, the level of unwanted emissions increases.
Another drawback of known valve seal assemblies is that the seal element is positioned too close to the valve guide. During operation of the engine, the valve stem of the valve becomes damaged with notches and burrs as it reciprocates within the valve guide. When the notches and burrs travel back and forth across a lip on the sealing element, the lip is damaged resulting in reduced operating life and effectiveness of the valve seal assembly.
SUMMARY OF THE INVENTION
The present invention is embodied in a valve seal assembly used to prevent the fluid used to lubricate a valve stem and a valve guide in an internal combustion engine from entering the combustion chamber of the engine. The valve seal assembly has an outer side surface that is sealingly engaged with an engine housing. The valve seal assembly may also include a resilient sealing element that has an improved sealing lip. The improved sealing lip is sealingly engaged with the valve stem in order to prevent the lubricating fluid from escaping past the sealing lip. The sealing lip is also positioned relative to the valve guide in order to extend the operating life and effectiveness of the sealing element. The valve seal assembly of the present invention comprises a shell and the resilient sealing element. The shell preferably includes a retainer wall that extends inwardly from a first end of the shell. The resilient sealing element is disposed within an opening in the retainer wall, preferably by engaging a notch in the sealing element with an edge in the opening of the retainer wall. The shell is preferably a cylindrical shell.
The sealing element further includes an improved sealing lip that is sealingly engaged with the valve stem. The sealing lip is located axially outside of the shell adjacent to the first end. The sealing lip extends from the valve stem (i) toward the shell, preferably at an angle between 30° and 90° relative to the valve stem, and (ii) away from the shell, preferably at an angle between 10° and 60° relative to the valve stem. A ring-shaped spring may also be disposed about the sealing element to compress the sealing lip against the valve stem.
The present invention has another aspect in that the valve seal assembly may be part of an apparatus that substantially prevents lubricating fluid from escaping an engine housing. The apparatus includes the valve seal assembly, an engine housing, and a guide disposed about the valve stem within the engine housing. The guide directs the reciprocating movement of the valve stem along a longitudinal axis of the valve stem. The valve seal assembly is preferably disposed near the end of the valve guide that is closest to the combustion chamber (i.e., the port side). Locating the valve seal assembly near the end of the valve guide closest to the combustion chamber substantially prevents the lubricating fluid from entering the valve ports yet allows complete lubrication of the valve stem and valve guide.
The valve seal assembly may also include a shell that has an outer side surface adapted to be sealed against an engine housing. The outer side surface is preferably sealed by a press fit, against a machined (i.e., substantially smooth) surface on the engine housing. Even more preferably, the machined surface of the engine housing is an inner side surface of a counterbore that has been machined into the engine housing. The inner side surface of a counterbore is substantially smooth when machined by known cutting techniques. This substantially smooth inner side surface provides an effective seal in conjunction with the outer side surface of the shell when the shell is pressed or disposed in the counterbore.
Another aspect of the present invention pertains to the location of the sealing lip on the valve seal assembly. The sealing lip is sealingly engaged with the valve stem and is positioned such that no substantial part of the valve stem which reciprocates within the guide touches the lip. Locating the lip of the sealing element in this manner serves to prevent the sealing lip from being harmed by any significant portion of the valve stem that might have been damaged as a result of the reciprocating movement within the valve guide. Since only undama
Benton Jason
Briggs & Stratton Corporation
McMahon Marguerite
Michael & Best & Friedrich LLP
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