JPH06193504A - Resin made piston - Google Patents

Abstract

PURPOSE:To improve an abrasion resistance as a resin made piston and improve its productivity by forming the top part of a piston with the top of a metallic material made piston, and using heat-proof resin mixed with lubricant for a skirt part. CONSTITUTION:A resin made piston is constituted in such a way that a metallic material made piston top part 1 which is brought contact with a combustion chamber is integrated with a skirt part 2 constituted by heat-proof resin including lubricant. The heat proof resin used here is of at least one kind selected out of polyimide resin, condensed polycyclic multinuclear aromatic resin, polyamide-imide resin and phenolic resin. Fine particle shaped lubricant which is at least one kind selected out of graphite, molybdenum disulfide, organic molybdenum compound and fluoro resin is compounded within a range of 5 to 70weight% into this heat-proof resin. It is thus possible to apply the heat proof resin in a piston operated in such a condition as being very strict in both thermal and sliding view, and also improve heat resistance, abrasion resistance, and productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin piston for a reciprocating engine.

[0002]

2. Description of the Related Art In a reciprocating engine, a lightweight piston is required in order to improve the output by increasing the rotation speed, reduce the hitting noise of the piston and the cylinder, reduce the sliding resistance between the piston and the cylinder, improve fuel consumption and oil consumption. ing. Conventionally, a method of applying a resin material having a low specific gravity has been attempted as one means for reducing the weight of the piston. For example, JP-A-56-88934, JP-A-57-105541,
JP-A-58-212155, JP-A-1-142245
JP-A-2-271059 discloses an invention in which a fiber-reinforced resin reinforced with carbon fiber or glass fiber is applied as a resin material.

However, the fiber-reinforced resin has a problem of poor lubricity, and as an invention to improve this, a resin layer having excellent lubricity is formed on the surface layer of the piston portion that slides with the cylinder, as disclosed in JP-A-60-67750. There is JP-A-60-79142 or JP-A-3-267552 in which a metal coating is formed on the surface layer of the skirt portion of the piston. In addition, a resin layer is formed on the surface layer of the skirt portion of the piston that slides on the cylinder for the purpose of reducing the sound of the piston hitting.
There is an invention of -108850.

[0004]

When a resin material is used for the piston, the characteristics required of the resin material include not only mechanical and thermal characteristics that can withstand operation but also wear resistance and productivity. To be Further, in the case where the fiber reinforced resin is used as the resin material, there is a defect that abrasion resistance and productivity are poor. In particular, when long fibers are used as the reinforcing fibers, the mechanical properties are improved, but there is a problem that it takes time for molding and is not suitable for mass production. Further, as a method of improving the abrasion resistance of the fiber reinforced resin, in the case of coating the surface thereof with a resin having excellent sliding characteristics, a step of further forming a resin layer in the production process of the fiber reinforced resin having originally low productivity. Therefore, the wear resistance is improved, but the productivity is further deteriorated.

The object of the present invention is to solve the above-mentioned problems of the conventional device, to be excellent in productivity, to be easily mass-produced, and to be lighter in weight than the conventional metal piston, so that the engine performance is low in noise and easy to start. The purpose of the present invention is to provide a resin-made piston that can realize improved efficiency, reduced sliding resistance loss, reduced oil consumption, and improved fuel efficiency.

[0006]

The resin piston of the first invention is characterized in that it has a piston top made of a metallic material and a skirt portion made of a heat-resistant resin containing a lubricant, In the second invention, at least one kind of the heat resistant resin is selected from polyimide resin, condensed polycyclic polynuclear aromatic resin, polyamide resin and phenol resin, and graphite, molybdenum disulfide, organic molybdenum compound and fluorine are selected. The resin piston according to the first aspect of the invention is characterized in that at least one kind of fine powder lubricant is selected from the resins in an amount of 5 to 70% by weight.

The resin forming the skirt is a heat resistant resin having mechanical properties, heat resistance, wear resistance, and self-lubricating property with excellent productivity. This piston has a simple structure, and a lightweight piston can be manufactured by a molding method having excellent productivity such as injection molding, transfer molding, and compression molding.
The present invention will be described in more detail with reference to specific examples of the piston, but the present invention is not limited thereto. Displacement 24 cc (piston diameter 32 mm, stroke 30
mm) single cylinder two-cycle engine will be described as an example of the present invention. When operating at a rotation speed of 8000 rpm, the maximum pressure in the combustion chamber is about 27k, depending on the type of engine.
Reach gf / cm ² . The force acting on the piston is an inertial force due to this gas pressure and the weight of the piston, and it is complicated because these forces change momentarily with the rotation of the crankshaft, but the force acting on the piston is almost maximum. When the maximum pressure is reached in the combustion chamber, the value reaches 160 kgf. This force is divided into a surface pressure applied to the sliding surface of the piston and the cylinder and a load applied to the connecting rod according to the inclination of the connecting rod. Of these, the problem is the surface pressure applied to the sliding surface, which is about 2.5 kgf / cm ² (maximum). On the other hand, the sliding speed on the sliding surface of the piston and cylinder is 8000r.
It is about 13 m / s (max) in pm. Generally, the PV value (product of surface pressure and sliding speed), which is a problem for sliding members, is about 27k when the piston weight is 35g and the piston is 8000rpm.
It is gf / cm ² m / sec.

In order to apply the resin material to the skirt portion of the piston that slides on the cylinder, it is required that the abrasion resistance be good at the PV value. The fiber reinforced resin reinforced with glass fiber or carbon fiber as the reinforced fiber has a drawback that abrasion resistance is poor because the fiber in the resin scrapes the mating material with which the fiber is in sliding contact. On the other hand, in the case of a resin alone containing no reinforcing fiber, the abrasion resistance is deteriorated because the resin is also soft against the sliding surface of the cylinder. Therefore, in the present invention, as a result of studying a resin composition which is excellent in abrasion resistance and does not damage a sliding material such as a fiber reinforced resin, at least one selected from graphite, molybdenum disulfide, an organic molybdenum compound or a fluororesin. It was found that the resin material in which the fine powdered lubricant is mixed with the resin is good.
If the amount of the lubricant is less than 5% by weight, the abrasion resistance of the resin is poor, and if it exceeds 70% by weight, the mechanical strength of the resin is significantly impaired.
It has been found that a range of is desirable.

Further, the resin applied to the piston of the internal combustion engine is required to have high heat resistance. In particular, when a resin piston is used in an air-cooled two-cycle engine, the temperature of the piston skirt is known to reach approximately 250 ° C during operation, and the piston top is made of aluminum alloy and the skirt is made of resin. In the case of the structure, since the resin has a low thermal conductivity, the diffusion of heat is hindered, and the temperature at the top of the piston reaches 300 ° C. or higher. Therefore, it is about 3 as a resin that can be applied to the piston of a two-cycle engine that is thermally severe.
Heat resistance close to 00 ° C is required. Examples of resins satisfying the above requirements include polyimide resins, condensed polycyclic polynuclear aromatic resins, polyamideimide resins and phenol resins. It has been found that compositions in which a lubricant such as graphite is further added to these resins in the range of 5% by weight to 70% by weight have excellent wear resistance, and these compositions are applicable to engine pistons. It was confirmed.

A graphite lubricant can be added to these resin compositions, but a commercially available product containing graphite in advance can also be obtained. Describing with specific examples thereof, an SK range (trade name) in which graphite is mixed with a condensed polycyclic polynuclear aromatic resin is suitable. These resins can be molded into the shape of the skirt portion of the piston with good productivity by a known molding method such as injection molding or compression molding. These resin compositions have a specific gravity of 1.3 to 1.7, which is lighter than the conventionally used aluminum alloy having a specific gravity of about 2.7. Therefore, the weight of the piston can be significantly reduced. When the piston skirt portion 2 made of an aluminum alloy is made of a polyimide resin containing graphite, the weight can be reduced by about 20% as compared with the conventional aluminum light alloy.

[0011]

Since the top of the piston is formed by the top of the piston made of a metal material and the skirt is made of a heat resistant resin mixed with a lubricant such as graphite as in the above-mentioned means, it is slid on the cylinder as in the conventional case. Since it is not necessary to coat the surface of the skirt portion of the piston in contact with the resin composition having excellent wear resistance, productivity is improved. Further, the composition of the resin forming the skirt portion of the piston shown in the second invention can be sufficiently applied to the piston of a two-cycle engine which is excellent in heat resistance and productivity and is severe in thermal or lubrication. Therefore, according to the present invention, it is possible to manufacture a piston for an engine which is lightweight and has excellent productivity.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing the piston construction of the first and second embodiments. [First Example] A piston top portion 1 including a piston ring groove was manufactured using aluminum alloy AC2B-T6. A female thread for joining was machined inside the top of the piston. A piston skirt portion was molded by a compression molding method using a polyimide resin containing graphite (TI-3110, Toray Industries, Inc.) and, at the same time, a male screw was formed on the piston skirt portion. Next, the piston top portion 1 and the piston skirt portion 2 were integrally fastened with a screw, and a knock pin was struck in the piston ring groove to fix both. The piston with a diameter of 32 mm created in this way was installed in a 2-cycle engine with a displacement of 24 cc.
It was operated for 100 hours at 000 rpm, but the operation could be completed without any abnormality.

[Second Embodiment] The piston top portion 2 is made of aluminum alloy AC2B-T6 as in the first embodiment, and has a knurled surface (mesh-like jagged surface) for preventing spillage. The piston skirt was molded by an injection molding method using a condensed polycyclic polynuclear aromatic resin containing graphite (SK Range-L, Sumikin Co., Ltd.) to obtain an integrated piston. 32mm diameter created in this way
The piston was installed in a two-cycle engine having a displacement of 24 cc and operated at 8000 rpm for 100 hours. No abnormality occurred, and the operation was safe.

[0014]

Since the present invention is configured as described above, it can be applied to a piston operated under severe thermal and sliding conditions, such as an air-cooled two-cycle engine, and has heat resistance, wear resistance and It is possible to mass-produce the piston of the internal combustion engine, which is excellent in productivity, has a simple structure and is lightweight, and can be manufactured at low cost. Further, since the resin piston of the present invention is lighter than the conventional metal piston, it has effects of reducing noise, facilitating starting, reducing sliding resistance loss, reducing oil consumption, and improving fuel consumption.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional configuration diagram of a piston according to a first embodiment of the present invention.

[Explanation of symbols]

1 ... Piston top part, 2 ... Piston skirt part, 3 ... Screw or knurling part.

Claims (2)

[Claims] 1. A resin piston having a piston top made of a metal material, which is in contact with the combustion chamber, and a skirt portion made of a heat-resistant resin containing a lubricant. 2. The heat-resistant resin is at least one selected from a polyimide resin, a condensed polycyclic polynuclear aromatic resin, a polyamideimide resin, and a phenol resin. Graphite, molybdenum disulfide, an organic molybdenum compound. 2. The resin piston according to claim 1, wherein at least one kind of fine powdery lubricant selected from the fluororesin is blended in the range of 5% by weight to 70% by weight.