1. Field of the Invention
This invention relates to pistons and cylinder liners for use in reciprocating engines and compressors.
2. Description of the Prior Art
Reciprocating internal combustion engines have been almost universally used in road vehicles since before 1900, and it has been the practice to use aluminum alloy pistons in cast-iron cylinders or cylinder liners. Steel inserts in aluminium alloy pistons first came into use in the Nelson Bohnalite piston of 1927, and were also used in the pistons of the Junkers Jumo 203 engine of 1930; similar inserts were employed in the Mahle Autothermic design of piston of 1935, and various manufacturers have employed steel inserts in aluminium alloy pistons from then until the present day. The purpose of these inserts is to modify the thermal expansion characteristics of the piston, and the running surface of the skirt of all such pistons that were successfully used was of aluminium alloy, the cylinder bore being of cast iron. Examples of aluminium alloy pistons having steel inserts for the control of thermal expansion may be found in British Pat. Nos. 701,291, 1,134,245 and 1,394,830.
More recently, aluminium alloy cylinder blocks have been introduced, and where aluminium alloy pistons are to be used in aluminium alloy cylinders, one of several choices is employed. Either one of the surfaces (i.e. the piston skirt or the bore) is coated, for example by electroplating with chromium or another coating compatible in operation with a co-operating aluminium alloy surface; or a special aluminium alloy, e.g. one treated with graphite, is employed for the cylinder; the latter is significantly more expensive than the more usual aluminium silicon alloys; or in a further example, a special etching treatment is used on the cylinder wall, but this is not altogether satisfactory under low temperature conditions, such as when starting the engine in cold weather.