Internal-combustion engines – Particular piston and enclosing cylinder construction – Piston
Reexamination Certificate
1999-08-11
2001-02-20
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Piston
Reexamination Certificate
active
06189500
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a piston for an internal combustion engine comprising an essentially cylindrical body with a plurality of axially spaced ring grooves in its lateral surface spaced from an end surface, a first portion of the cylindrical body, lying between the end surface and the most closely adjacent ring groove, having varying cross section.
DESCRIPTION OF THE RELATED ART
It is a known fact that pistons for internal combustion engines change their shape during engine operation under the influence of heat in the combustion chamber and the occurrence of dynamic forces.
The shape of the piston in its cold state must therefore be adapted to these changes in shape so that there is maintained between the piston and the cylinder wall, a clearance which is neither so small as to risk polishing of the cylinders when coke is deposited on the piston, nor so large that emissions and performance are negatively affected. Cylinder polishing results in increased oil consumption and can result in shearing.
The shape of the piston must also be adapted to those changes in shape which occur in the engine block itself as it is heated, which results in the outer cylinders in a multicylinder engine becoming inclined relative to the center cylinders. In other words, the cylinders will assume a “fan” shape as the engine block is heated and expands more at the top than at the bottom during engine operation.
In order to adapt the shape of the piston to this changing shape in the engine block, it is common to make the piston with an oval cross section with the minor diameter oriented in the longitudinal direction of the engine. The difference between the major and minor diameters of this piston portion is, in previously known engine designs, not larger than about 0.15 mm, which means a “normal” so-called top ring land clearance in the transverse direction of the engine of 0.40 mm and in the longitudinal direction of 0.55 mm when the engine is cold. In a known engine with a 131 mm cylinder diameter, this means a difference between the major and minor diameters which is about 0.1% of the major diameter. This clearance has, however, in certain engine designs not proved to be sufficient to eliminate the risk of polishing of the cylinders. It is a known fact that a small top ring land clearance can increase the risk of polishing the cylinder. This can be avoided by providing the piston with a large top ring land clearance. The clearance in this case has amounted to about 2 mm, which has, however, led to a large detrimental volume having a negative effect on emissions and performance.
SUMMARY OF THE INVENTION
The purpose of the present invention is to achieve a piston of the type described by way of introduction, by which it is possible to avoid cylinder polishing without making the detrimental volume so large that emissions and performance are affected more than marginally.
This is achieved according to the invention by virtue of the invention that the difference between the major and minor diameters of the cross section of the top ring land of the piston is at least 0.3% of the major diameter.
The invention is based on the idea of first investigating where cylinder polishing occurs and having a top ring land ovality which provides as little clearance as possible where no polishing occurs and increases the clearance only so much in the polished cylinder portions that polishing is avoided. Tests performed have shown that for a given engine design, polishing could not be avoided with common top ring land ovality on the order of 0.15 mm, i.e. about 0.1%, while it was only possible to eliminate polishing from 0.3%.
REFERENCES:
patent: 1462501 (1923-07-01), Barwald
patent: 2311039 (1943-02-01), Emery
patent: 4111104 (1978-09-01), Davison
patent: 4256022 (1981-03-01), Elsbett et al.
patent: 4716817 (1988-01-01), Ripberger et al.
patent: 4829955 (1989-05-01), Strasser
patent: 5072653 (1991-12-01), Parsons
patent: 5211101 (1993-05-01), Letsch et al.
patent: 5245913 (1993-09-01), Kato
patent: 755235 (1951-08-01), None
AB Volvo
McMahon Marguerite
Young & Thompson
LandOfFree
Internal combustion engine piston does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Internal combustion engine piston, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Internal combustion engine piston will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593427