Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-09-20
2002-09-24
Cuda Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
Reexamination Certificate
active
06453555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of producing a piston for a compressor which compresses a gas, and more particularly to a method of producing such a piston having a hollow cylindrical head portion which is slidably fitted in a cylinder bore formed in a cylinder block of the compressor.
2. Discussion of the Related Art
A piston used for a compressor is reciprocated within a cylinder bore formed in a cylinder block of the compressor. In view of this, it is desirable to reduce the weight of the piston. When the piton is used for a swash plate type compressor, in particular for a variable capacity type swash plate compressor, it is particularly required to reduce its weight. As the swash plate type compressor for compressing a refrigerant gas used in an air conditioning system of an automotive vehicle, the above-described variable capacity type swash plate compressor has been recently used, wherein the angle of inclination of the swash plate with respect to a plane perpendicular to the axis of rotation of the drive shaft is variable to change the discharge capacity of the compressor. In the swash plate type compressor for the vehicle, it is generally required to increase a rotation speed of the drive shaft for thereby attaining an improved operating performance of the compressor, so as to meet the demand for reducing the size of the compressor. To this end, it is necessary to reduce the weight of the piston. In the variable capacity type swash plate compressor wherein the angle of inclination of the swash plate is adjusted on the basis of a difference between the pressures in a compressing chamber which is partially defined by the piston, and a crank chamber in which the swash plate is disposed, it is particularly required to reduce the weight of the piston for achieving a stable adjustment of the inclination angle of the swash plate and reducing the noise of the compressor during its operation.
The assignee of the present invention proposes, in the Japanese Patent Publication No. 9-105380 and its corresponding U.S. Pat. No. 5,174,728, a technique of reducing the weight of the piston used for the variable capacity type swash plate compressor. Namely, the piston having a hollow head portion which is slidably fitted in the cylinder bore is produced, by first preparing a hollow cylindrical head member having an open end and a closed end, then closing the open end of the head member by a closure member which is formed integrally with an engaging portion which engages the swash plate, and finally welding the head member and the closure member together. The head member and the closure member are both formed by forging.
The formation of the head member and the closure member by forging inevitably pushes up a cost of manufacture of the piston. To reduce the cost, the piston with a hollow head portion is formed by die-casting. In the die-cast piston, however, it is difficult to weld the head member and the closure member to each other, and this problem makes the die-cast piston unsuitable for practical use. Further, it is desirable to reduce the weight of the piston in other types of the compressor such as a fixed capacity type as well as the variable capacity type.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of producing a piston for a compressor, wherein at least a hollow cylindrical head portion of the piston is formed by die-casting and a closure member is welded to the hollow cylindrical head portion.
The above object may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depends from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) According to a first feature of the present invention, there is provided a method of producing a piston for a compressor, comprising the steps of casting a molten material into a die to form a hollow cylindrical head portion of the piston that is open at one of opposite ends thereof and is closed at the other end thereof, such that an amount of gas included in the material of the head portion is not more than 5 cc per 100 g of the material; closing, with a closure member, the open end of the head portion; and welding the head portion and the closure member to each other by emitting, a plurality of times, a welding beam toward each of a multiplicity of spots on a welding line along which the head portion and the closure member contact each other.
In the present production method, it is desirable that the closure member be also formed by die-casting. However, this is not essentially required. The piston may include an engaging portion which is integrally formed with the closed end of the hollow cylindrical head portion and which engages a drive mechanism, and the closure member may be a cover member which just closes the open end of the head portion. In this particular case, the cover member may be produced by a method other than the die-cast method; such as machining of a commercially available common material, such as a bar-like material, or forging. It is desirable that the head portion and the closure member be formed of an aluminum alloy that has a small specific gravity and is easily die-cast. However, the head portion and the closure member may be formed of a different material such as a magnesium alloy.
In a conventional die-cast piston, the amount of gas included in the material of the hollow cylindrical head portion of the piston is 10 to 30 cc per 100 g of,the material under normal condition, i.e., one atmospheric pressure and room temperature. In contrast thereto, in a piston produced by a special die-cast, such as pore-free method or forging cast method, described later, the amount of gas included in the material of the hollow cylindrical head portion of the piston can be lowered to 5 cc per 100 g of the material udder the normal condition. The open end of the head portion is closed with the closure member, and the head portion and the closure member are welded to each other by emitting a welding beam, two or more times, toward each of a number of spots on a welding line along which the head portion and the closure member contact each other, so that respective welded portions of the head portion and the closure member have only a small amount of blowholes. The thus produced piston is suitable for practical use. The welding beam, such as an electronic beam or a laser beam, may be emitted to form a beam spot on the welding line, and one of the welding beam and the combination of the head portion and the closure member may be rotated relative to the other to move the beam spot on the welding line. Thus, respective welding portions of the head portion and the closure member, in the vicinity of the welding line, are molten and bonded to each other. At this Time, the gas included in the material of the members are heated and expanded to run away into the atmosphere, so that blowholes are produced in the welding beads. However, since the amount of pas included in the material is at the low level of not more than 5 cc per 100 g of the material, the amount of the blowholes produced is also at a low level. In addition, the blowholes which arc once produced in the welding beads are closed when the welding beads are subjected to another exposure to the welding beam and are molten, so that the welding beads have a still less amount of blowholes. The thus produced die-cast piston is highly suitable for practical use The phrase of “emitting, a plurality of times, a wel
Katayama Seiji
Kato Takayuki
Cuda Rosenbaum I
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Woodcock & Washburn LLP
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