JPH05312266A - Piston - Google Patents

Abstract

PURPOSE:To prevent seizure of a piston skirt with the wall surface of a cylinder and also reduce frictional resistance by coating a part of the outer peripheral surface of the piston skirt with ceramics materials. CONSTITUTION:Ceramics materials 7 of CrN or TiN of which plane form is, for example, square and with a desired thickness are coated on the outer peripheral surface of a piston skirt 2a at desired intervals and in grid-like pattern. Distances between the ceramics materials 7 are provided to prevent thermal stress from generating due to different thermal expansion between the constituent material of a piston 2 and the ceramics materials caused when the piston 2 is heated at high temperature during the operation, resulting in cracks of the ceramics materials. Because the surface of the ceramics materials 7 and the wall surface of a cylinder are made in contact slidably with each other, and the outer peripheral surface of the piston skirt 2a is not directly made in contact slidably with the wall surface of the cylinder, seizure of the piston can be prevented. Also, because a coefficient of friction between the surface of the ceramics materials 7 and the wall surface of the cylinder is small, a frictional loss between them is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston which is a part incorporated in an automobile engine, and more particularly to a piston which has reduced frictional resistance with a cylinder wall surface.

[0002]

2. Description of the Related Art In an automobile engine, as shown in FIG. 3, a piston 2 is slidably accommodated in a cylinder 1 and an airtight combustion chamber 3 is formed in an upper portion thereof. It is connected to the crankshaft 5 through the structure. In the piston 2, the piston rings 6, 6, 6 fitted in the ring groove formed in the upper part of the piston 2 and the outer peripheral surface of the piston skirt 2a forming the lower part of the piston vigorously slide on the wall surface 1a of the cylinder 1. While moving, it reciprocates up and down in the cylinder 1 under a high heat environment.

[0003]

In order to prevent the piston skirt from sticking to the wall surface of the cylinder to cause scuffing, the outer peripheral surface of the piston is usually attached to the piston which reciprocates in the cylinder. For example, Sn plating is applied to increase the seizure resistance.

However, when an engine of higher output is developed by turbo supercharging or the like, the heat supplied by the engine exhaust exposes the piston to a more severe high temperature environment, so that the piston skirt is seizure-resistant. It is necessary to further improve the sex. Also, considering the friction loss during operation of the entire engine, about 1/100 of that
4 is the friction loss in the piston system. Of this friction loss of the piston system, about 2/3 occurs between the piston ring and the wall surface of the cylinder, and the remaining about 1/3 occurs between the piston scard and the wall surface of the cylinder. ..

Therefore, it is important to reduce the above-mentioned friction loss when an attempt is made to increase the engine output and fuel consumption. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a piston having a piston skirt that does not cause seizure with the wall surface of a cylinder and has a small frictional resistance with the wall surface of the cylinder.

[0006]

In order to achieve the above object, the present invention provides a piston characterized in that a part of the outer peripheral surface of a piston skirt is coated with a ceramic material.

[0007]

In the piston of the present invention, a ceramic material having a desired thickness is coated on a part of the outer peripheral surface of the piston skirt. Therefore, when the piston moves up and down, it is not the outer peripheral surface of the piston skirt that slides on the wall surface of the cylinder but the ceramic material coating surface. Since the ceramic material has excellent heat resistance and slidability, the frictional resistance between the piston skirt and the cylinder wall surface is reduced, and the friction loss in the piston system is reduced. Further, although the cylinder is generally made of Al alloy or cast iron, mutual welding of these metals and the ceramic material does not occur, so that the problem that the piston skirt is seized on the wall surface of the cylinder hardly occurs.

Therefore, the seizure resistance of the piston is improved, the friction loss is reduced, and the engine output is further increased.
It becomes possible to realize low fuel consumption.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A piston according to an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 3 is provided on the top of the piston 2.
A ring groove 2b of a book is provided around which a piston ring (not shown) is fitted. The outer peripheral surface of the piston skirt 2a is coated with a ceramics material 7 having a quadrangular planar shape and having a desired thickness in a state of being arranged in a lattice pattern with a desired interval therebetween. In this case, the planar shape of the ceramic material 7 is not limited to a quadrangle, but may be any shape such as a circle.

A space is provided between the ceramic members 7 so that, for example, when the entire outer peripheral surface of the piston skirt 2a is coated with the ceramic member, if the piston 2 becomes hot during operation, Two
Due to the difference in thermal expansion between the Al alloy or cast iron, which is the constituent material of the above, and the ceramics material, thermal stress is generated between the piston and the ceramics material, resulting in cracks in the ceramics material coating the entire piston skirt. This is to prevent the problem of the ceramic material peeling off when it occurs.

The ceramic material is not particularly limited as long as it has good heat resistance and slidability and can coat the outer peripheral surface of the piston skirt. For example, CrN and TiN are good materials. Is. The piston skirt can be coated with these ceramic materials by applying, for example, an ion plating method.

That is, the piston is put in an ion plating device, the outer peripheral surface of the piston skirt is cleaned by Ar ⁺ glow discharge, and then the gas introduced into the device is replaced with N 2.
₂ gas is switched to form N ⁺ glow discharge, and Cr is evaporated from, for example, a Cr evaporation source set in the apparatus, and Cr is ionized by the above-mentioned N ⁺ , and at the same time, it is formed on the outer circumference of the piston skirt. A CrN layer having a desired thickness is formed by depositing CrN on the surface.

Since the coating surface of the ceramic material 7 thus formed is projected from the outer peripheral surface of the piston skirt 2a, the surface of the ceramic material 7 and the wall surface of the cylinder are in sliding contact with each other during operation of the piston. The outer peripheral surface of the piston skirt 2a does not directly contact the wall surface of the cylinder. Therefore, seizure between the wall surface of the cylinder and the outer peripheral surface of the piston skirt 2a is effectively prevented, and the friction coefficient between the surface of the ceramic material 7 and the wall surface of the cylinder is small. 7 is reduced as compared with the case where it is not coated.

For example, referring to FIG. 1, the ceramic material 7
As a result of the above-mentioned ion plating method,
The tendency of the friction coefficient between the piston skirt and the cylinder wall when the CrN layers with a width of 3 mm and a thickness of 1 μm are arranged in a grid pattern at an interval of 1 mm and the friction coefficient when the ceramic material is not coated are shown. As shown in FIG. In the figure, the solid line represents the tendency of the example and the broken line represents the tendency of the comparative example.

As is apparent from FIG. 2, in the piston of the embodiment, the frictional resistance is greatly reduced and at the same time, the increase in the frictional resistance is also smaller than that of the piston in which the CrN layer is not formed.

[0016]

As is apparent from the above description, the piston of the present invention is characterized in that a part of the outer peripheral surface of the piston skirt is coated with a ceramic material. The surface of the material comes into sliding contact with the wall surface of the cylinder. Therefore, the seizure between the piston skirt and the wall surface of the cylinder is effectively prevented from causing scuffing, and the friction resistance between the ceramic material and the wall surface of the cylinder is small, so that the friction loss in the piston system is reduced.

From the above, the piston of the present invention has great industrial value as a piston for an engine with high output and low fuel consumption.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment piston of the present invention.

FIG. 2 is a graph showing a friction coefficient between a piston and a wall surface of a cylinder.

FIG. 3 is a schematic diagram showing a configuration of an engine.

[Explanation of symbols]

 1 Cylinder 1a Cylinder wall 2 Piston 2a Piston skirt 2b Ring groove 3 Combustion chamber 4 Connecting rod 5 Crankshaft 6 Piston ring 7 Ceramics material

Claims (3)

[Claims] 1. A piston characterized in that a part of the outer peripheral surface of the piston skirt is coated with a ceramic material. 2. The ceramic material is CrN or T
The piston of claim 1 which is iN. 3. The piston according to claim 1, wherein the coating of the ceramic material is performed by an ion plating method.