Expansible chamber devices – Piston – Open-ended hollow skirt type
Patent
1995-05-26
1996-10-01
Denion, Thomas E.
Expansible chamber devices
Piston
Open-ended hollow skirt type
92208, F16J 104
Patent
active
055602835
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the running surfaces of a piston and a cylinder of an internal combustion engine.
2. The Prior Art
With piston-cylinder assemblies of said known type, the running layer of the piston is normally a metallic-type layer which is applied galvanically.
Based on the above, the invention deals with the problem of creating an economically producible piston running layer, whose properties are at least equal to the coatings applied galvanically heretofore.
SUMMARY OF THE INVENTION
A solution to said problem is provided, according to the invention by a piston having at least one piston ring in combination with a cylinder of a two-stroke internal combustion engine. The piston-cylinder combination is comprised of a piston made from an aluminum alloy including a running surface with a running layer covering at least 80% of said running surface. The running layer is made from resin-bound graphite. The piston ring has a crowned running surface and is made from cast iron or steel. The cylinder includes a running surface where at least the running surface is made from an aluminum alloy, wherein the running surface has a roughness of R.sub.a of less than one (1) micron.
Alternatively, the roughness R.sub.a is less than eight-tenths (0.8) of a micron or less than one-half (0.5) of a micron. In a further embodiment, the roughness R.sub.a is less than or equal to three-tenths (0.3) of a micron. The aluminum alloy forming the running surface of the cylinder is an aluminum-silicon alloy having a silicon content which is greater than eight percent (8%) by weight. The aluminum alloy forming the running surface of the cylinder is an aluminum-silicon-zinc alloy having a silicon component which is greater than five percent (5%) by weight and a zinc component which is greater than two percent (2%) by weight. The running surface of the cylinder is precisely drilled.
The running surface of the piston has a thickness between ten (10) and twenty (20) microns. The resin-bound graphite forming the running layer includes graphite particles having a size between one (1) and ten (10) microns or alternatively, a size between one (1) and five (5) microns. The resin-bound graphite has a graphite content between thirty percent (30%) and sixty percent (60%) or, alternatively a graphite content between forty percent (40%) and sixty percent (60%).
The resin-bound graphite includes a resin vehicle made from curable polyimide. The running layer of said piston is a cured running layer which is cured between 150.degree.-200.degree. C. for between 10-30 minutes. The aluminum alloy forming said piston is an aluminum-silicon alloy.
The R.sub.a -value specified in the claims is a value fixed according to the ISO-standard and denotes the arithmetic mean of the peak heights of the surface peaks forming the roughness. The piston-cylinder assembly according to the invention is intended for use particularly in connection with internal combustion engines for lawn mowers, motorized cutters, tractor-drawn cutters, and stationary engines.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a cross-sectional view through a piston-cylinder assembly according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The piston 1 has a diameter of about 42 mm and is guided in a cylinder of a two-stroke engine. The basic material of the piston consists of an aluminum alloy, for example an aluminum-silicon alloy having the following composition stated in percent by weight:
______________________________________ Si 17-19
Cu 0.8-1.5
Mg 0.8-1.3
Ni 0.8-1.3
Fe less than or equal to 0.7
Mn less than or equal to 0.2
Ti less than or equal to 0.2
Zn less than or equal to 0.3
Al balance
______________________________________
A running layer 3 made of graphite bound in resin is applied to each of the supporting zones of the piston skirt. These zones oppose each other in the pressure and counterpressure directions. A corresponding additional layer 4 can be applied to the
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Motortechnische Zeitschrift 34; (1973), Book 2, pp. 49 to 51.
Denion Thomas E.
Mahle GmbH
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