WO1988000289A1

WO1988000289A1 - Piston rings

Info

Publication number: WO1988000289A1
Application number: PCT/AU1987/000207
Authority: WO
Inventors: Robert Walter Vowles
Original assignee: ENGINE TECHNOLOGY Ltd
Current assignee: ENGINE TECHNOLOGY Ltd
Priority date: 1986-07-09
Filing date: 1987-07-09
Publication date: 1988-01-14
Anticipated expiration: 1989-01-09

Abstract

An improved design of compression piston ring (3) for use in internal combustion reciprocating engines, the piston ring (3) having a peripheral cylinder engaging surface (6) with an edge zone (7) adapted to face towards a combustion zone of the engine cylinder (4), the edge zone (7) forming a layer having a hardness or wear resistance greater than the remainder of the peripheral surface, the said remainder of the peripheral surface, at least during initial use, being textured to provide a multiplicity of small contact areas which may wear more quickly than said edge zone (7), alignment of the piston ring (3) may be ensured by having the piston ring groove (8) made of a material of greater wear resistance than the remainder of the piston (2).

Description

PISTON RINGS

The invention concerns improvements in compression piston rings for piston internal combustion engines.

In piston internal combustion engines, compression piston rings are provided to prevent leakage of combustion-generated pressure from the combustion chamber past the piston into the crankcase. Cylinder leakage results in a decrement in engine performance and efficiency due to the loss of gas pressure.

Additionally and more importantly, it reduces engine life as a result of overheating due to transfer of heat to the cylinder walls, contamination of lubricant resulting in increased wear rates, and damage to pistons resulting from overheating and accumulation of deposits of burned oil.

In conventional compression piston ring designs, attention is usually given to the maximisation of pressure against the cylinder bore of the lower edge of the ring, that is to say, the edge of the ring nearest the crankcase. This is to ensure the existence of a scraping effect which minimises the quantity of lubricating oil which finds its way to the combustion chamber. Increased cylinder bore pressure of the lower edge of the piston ring is generally achieved by tapering the cylinder bore contact face or by chamfering or counter-boring the inner upper edge of the ring to obtain a relaxation of pressure at the upper part of its contact face.

In the modern engine, in which oil contol piston rings are efficient, the requirement for the compression piston ring to exert a cylinder bore scraping effect is redundant. At the same time, it can be demonstrated that cylinder leakage is common in the modern mass-produced piston engine. It can also be demonstrated that positive sealing of the compression piston ring depends upon the maintenance of a sharp upper edge of the ring, and that sealing is effected by a very narrow band at the upper edge of the piston ring cylinder bore contact face. As the compression piston ring wears, cylinder bore contact pressure is diminished, its upper edge becomes worn and slightly rounded and cylinder leakage commences. This process is accelerated in the above entioned design of _c piston ring, because of the tendency to reduce the cylinder bore contact pressure of the upper edge of the ring.

The present invention aims at providing an engine compression piston ring which substantially extends the life of an engine by minimising the development of cylinder _{* Q} leakage caused by wear.

According to the present invention there is provided a compression piston ring for an engine defining a peripheral face adapted to engage an engine cylinder wall, said ring being characterized by a peripheral edge adapted _{1 ς} to face toward a pressure zone of said cylinder being more resistant to wear than the remainder of the peripheral face of the said ring. Preferably the said wear resistant peripheral edge is formed by a thin zone of either a different material to the remainder of the ring or by the

20 same material as the remainder of the ring treated in an appropriate manner to provide said relatively wear resistant characteristic.

According to a second aspect of the present invention there is provided an engine compression piston ring for use in an engine cylinder defining a peripheral

25 face divided into a first zone adjacent, in use, a pressure side of said cylinder and a second zone adjacent a crankcase side of said cylinder, said second zone, at least during initial stages of use being adapted to wear at a faster rate than said first zone. Conveniently said second zone is

30 initially textured to provide a multiplicity of small contact areas which may wear more quickly. In a particularly preferred arrangement the first zone is arranged to be harder or more wear resistant than the second

35 ^ZOne* Initial service of the engine will result in rapid wear of the said multiplicity of small contact areas, ensuring that maximum cylinder bore contact pressure is quickly developed at the hardened upper edge of the piston ring. The hardness of the piston ring upper surface ensures that a sharp upper edge of the piston ring is maintained and the differential wear rates resulting from the difference in hardness of the two zones of the piston ring ensures that subsequent wear in service maintains maximum cylinder bore contact pressure at the piston ring upper edge.

The present invention will be more readily understood by reference to the following description of a preferred embodiment given in relation to the accompanying drawing which represents a transverse sectional view of a piston ring and an immediate area of the piston and cylinder bore.

With reference to the drawing, compression piston ring 3 is accommodated within groove 8 in piston 2. The upper surface 7 of the said piston ring is made with a thin layer of material harder than the other parts of the ring, said layer being created by electroplating the surface with a harder material, by fusing to it a layer of harder material, or by treating it with ion implantation techniques or the like. Excepting for the hardened upper edge, the cylinder bore contact face 6 of piston ring 3 is made textured such that it comprises a large multiplicity of small contact areas. This may be achieved by a multiplicity of shallow grooves, by a knurled configuration or by any other suitable means.

In an embodiment not shown, the piston ring groove is made of a harder, wear resistant material cast into the piston, to ensure the alignment of the said piston ring.

The material from which cylinder block 1 or cylinder bore 4 are manufactured are selected to be compatible with the two piston ring materials. In operation, initial wear of the said large multiplicity of small contact areas in the relatively softer textured cylinder bore contact face of the said piston ring, ensures that maximum cylinder bore contact pressure is developed at the harder upper edge. This ensures good ring seal at the earliest possible point in the life of the engine. The hardness of the said piston ring upper edge ensures that it maintains its sharpness in service. The subsequent differential wear rates of the harder upper edge and the lower softer parts of the piston ring ensures that maximum cylinder bore contact pressure is maintained at the said upper edge. The provision of a harder piston ring groove cast into the piston limits any tendency of the piston jring to twist as a result of the difference in cylinder bore contact pressures between its upper and lower edges.

Claims

CLAIMS ;

1. A compression piston ring for an internal combustion engine defining an outer peripheral face adapted to engage a cylinder wall of said engine, said ring being characterized by a peripheral edge adapted to face toward a pressure zone of said cylinder being more resistant to wear than the remainder of the peripheral face of said ring.

2. A compression piston ring according to claim 1 wherein a first zone adjacent said peripheral edge is more resistant to wear than the remainder of said peripheral face of said ring.

3. A compression piston ring according to claim 2 wherein said ring is annular in shape and includes axial directed faces at either end of said outer peripheral face, said first zone extending across one of said axial directed faces.

4. A compression piston ring according to claim 3 wherein said first zone is formed by a plated material coating applied to said one axial directed face.

5. A compression piston ring according to claim 2 or claim 3 wherein said first zone is formed by modifying the material and/or the structure of a base material from which the ring is produced.

6. A compression piston ring according to any one of claims 2 to 5 wherein the outer peripheral face of said ring comprises said first zone and at least one other zone, said other zone or each of said other zones, at least during initial use, being adapted to wear at a rate faster than that of said first zone.

7. A compression piston ring according to claim 6 wherein the or each said other zone comprises a surface texture including a multiplicity of small contact areas adapted to wear more quickly.

8. A piston for an internal combustion engine including a piston ring according to any one of claims 1 to 7 wherein the piston ring is arranged in a holding groove made of a material of greater wear resistance than the remainder of said piston.