Expansible chamber devices – With lubricating means – Piston has lubricant retaining or conducting means
Reexamination Certificate
2001-05-03
2003-02-25
Look, Edward K. (Department: 3745)
Expansible chamber devices
With lubricating means
Piston has lubricant retaining or conducting means
Reexamination Certificate
active
06523456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to sliding members which can maintain sufficient amounts of lubricating oil between sliding surfaces of sliding members sliding with respect to each other and which can reduce sliding resistance and can effectively avoid production of an unusual noise therebetween. The present invention also relates to a piston for internal combustion engines, which can hold sufficient amounts of lubricating oil on the sliding surface with a sleeve.
2. Background Art
In order to reduce the sliding resistance of sliding members, fluorine compounds, silicon, or the like, have been added to the materials of sliding members, or alternatively, coatings made from materials such as molybdenum and fluorine resin have been provided heretofore. However, the former case cannot yield substantial reduction in sliding resistance, and the later case has problems in that the coating flakes off or wears.
In particular, in a piston for internal combustion engines (hereinafter referred to simply as a “piston”), a part of the explosive pressure in the combustion chamber is received by a piston ring which slides with respect to a sleeve. The position of the piston is maintained by contacting a skirt portion provided at the lower portion of the piston with the sleeve. Therefore, if the contact of the skirt portion with the sleeve is not smoothly performed, the sliding resistance increases, whereby the fuel consumption is increased, and an unusual noise is produced due to the contact of the piston with the sleeve in some cases.
Japanese Utility Model Applications, First Publications, Nos. 16451/77 and 193941/82 propose methods in which fine dimples are formed on a skirt portion of pistons by sandblasting or shot peening. It is known that these methods cannot yield the effect of avoiding production of an unusual noise.
In general, it is known that surfaces sliding with respect to each other initially undergo severe wear. The reason for this is that sharp edges formed by machining are worn initially, and such wear is called “initial wear”. The initial wear occurs while being integrally affected by several factors, such as the amount of lubricating oil supplied to the sliding surfaces, surface pressure exerted on the sliding surfaces, sliding speed, surface roughness of the sliding surfaces, and heat generated by the effects of these factors. The wear amount and the sliding resistance are reduced when these factors are balanced (running-in phenomenon). After the running-in phenomenon, large amounts of wear does not occur as long as the balance is not disrupted. However, when the supply of a lubricating oil or the relative speed of the sliding, or the like, changes greatly, heat generation, rapid wear, and macro deformation of the sliding surface may occur, and these may cause an unusual noise.
Therefore, the present invention is based on the initial wear on the sliding members, and it is object of the invention to provide sliding members having ideal surface properties after the initial wear. That is, the object of the invention is to provide sliding members in which the sliding is smoothly performed after the initial wear, and an unusual noise can be effectively avoided. Furthermore, another object of the invention is to provide a piston to which the sliding members are applied, so that the clearance between the skirt portion and the sleeve can be narrow, whereby the position of the piston can be stable, and tapping of the piston can be prevented, and noise and vibration are therefore suppressed. It is a further object of the invention to reduce the sliding resistance in an early stage by occurrence of initial wear in a short time in an initial stage of operation.
SUMMARY OF THE INVENTION
The present invention provides sliding members having a sliding surface and which slide with respect to each other in a sliding direction, the sliding surface of at least one of the sliding members comprising: a protrusion extending along a direction intersecting the sliding direction; and fine dimples provided on a surface of the protrusion. The protrusion preferably extends in a direction perpendicular or approximately perpendicular to the sliding direction. The present invention further provides a piston comprising: a piston body; a skirt portion provided on a side surface of the piston body; a protrusion provided on at least the skirt portion and extending along the outer circumference thereof; and fine dimples provided on a surface of the protrusion. The functions of the invention will be explained with reference to pistons in FIG.
1
A and other figures.
FIG. 1A
shows a surface of a skirt portion of a piston without dimples, which is shown by a computer generated illustration, and shows protrusions extending along the outer circumference of the piston body.
FIG. 1A
shows the state of the outer circumference of the piston body after machining. The protrusion is formed between recesses having a circular cross section. The machining can be performed such that the outer circumference of the piston body is cut by a bite when relatively feeding the piston body in the axial direction thereof. In this case, the protrusion spirals along the axial direction.
When initial wear occurs on the piston, the edge portion of the protrusion is worn away so as to be approximately trapezoidal in cross section as shown FIG.
1
B. The trapezoidal portion consists of a sliding surface and edge E formed at the peripheral portions thereof, and the edge E inhibits the lubricating oil accumulated in the recesses from being supplyed to the sliding surface which requires lubrication.
FIGS. 2A and 2B
show a cross section of the protrusion shown in
FIGS. 1A and 1B
, wherein
FIG. 2A
shows a status after machining and
FIG. 2B
shows a status after the initial wear. As is understood from
FIG. 2B
, the edge formed at the peripheral portion of the sliding surface after the initial wear functions as a spike, and the lubricating oil cannot be supplied at some portions. In this case, the temperature of the portions would be increased and cause an unusual noise.
FIG. 3A
shows a surface of a skirt portion of the piston according to the invention, which is shown by a computer generated illustration, and shows a protrusion extending along the outer circumference of the piston body and fine dimples formed on the surface of the protrusion. When initial wear occurs on the piston, the edge portion of the protrusion is worn away so as to be approximately trapezoidal in cross section as shown FIG.
3
B. The dimples form drain portions B at the peripheral portions of the sliding surface on the trapezoidal portion.
The functions of the dimples in the invention will be explained with reference to
FIGS. 5A and 5B
. As shown in
FIG. 5A
, the surface of the piston in the machine-finished state has plural V-shaped grooves extending along the outer circumference thereof when seen magnified. When lubricating oil is provided .to the surface and surface pressure is exerted thereto, the lubricating oil is easily accumulated at the bottom of the groove due to capillary effect rather than the top edge portion, so that an oil film is difficult to be formed and the sliding resistance is large. In contrast,
FIG. 5B
shows an embodiment of the dimple according to the invention. When lubricating oil is provided to such a surface, as shown in
FIG. 5C
, the dimple functions as an oil reservoir and accumulates oil droplet O. Therefore, the oil film S is maintained when surface pressure is exerted on the surface, and increase of the sliding resistance is thereby prevented.
According to the invention, each fine dimple accumulates the lubricating oil, and the lubricating oil can be easily supplied to the sliding surface through the drain portion B by reciprocal movement of the piston. Therefore, after the initial wear has occurred and the piston is fitted to the sleeve, the lubricating oil is supplied to the sliding portion to form an oil film, thereby lubricating the sliding surface and avoiding an unusual no
Ishizuka Kazuhisa
Kobayashi Shigemi
Murata Masashi
Ogihara Hidemi
Tsunashima Sakae
Honda Giken Kogyo Kabushiki Kaisha
Kershteyn Igor
Look Edward K.
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