The present invention relates to a hollow piston, which is reciprocated by rotation of a cam body that rotates integrally with a rotary shaft and a method for producing the same.
A piston disclosed in Japanese Patent Unexamined Publication No. Hei 11-107912 is hollow to reduce its weight. Such a hollow piston improves displacement control for variable displacement type compressors, which control the inclination angle of a swash plate by controlling the pressure in a crank chamber.
The weight of a hollow piston can be reduced by reducing the thickness of a wall surrounding the hollow portion. The pressure of refrigerant gas is applied to the head end of the piston, which reciprocates inside the cylinder bore.
The head end wall of the piston is flat. However, if the head end is too thin, the piston will not have the strength required to withstand the pressure in the cylinder bore.
An object of the present invention is to reduce the weight of a hollow piston by reducing the weight of the head end wall of the piston.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a hollow piston used in a compressor is provided. The piston is accommodated in a cylinder bore of the compressor. The piston includes an end wall. The end wall receives the pressure of the cylinder bore. The end wall having an outer end face and an inner end face that is opposite to the outer end face. A reinforcing protrusion is formed on the inner end face and is radially symmetrical.
The present invention may be applied to a method for manufacturing a hollow piston used in a compressor. The piston includes a head piece and a body piece that is coupled to the head piece. The head piece has an end wall that receives the pressure of a cylinder bore of the compressor. The body piece includes the remainder of the piston. The end wall has an outer end face and an inner end face that is opposite to the outer end face. The method includes preparing a mold for forming the head piece, wherein the mold is designed such that a temporary protrusion is formed on the inner end face, pouring molten metal into the mold, pushing the temporary protrusion before the molten metal solidifies to prevent formation of shrinkage cavities, and removing part of the temporary protrusion after the molten metal solidifies, wherein the remainder of the temporary protrusion serves as a reinforcing protrusion.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.