GB2163234A

GB2163234A - Improvements in or relating to piston rings and their manufacture

Info

Publication number: GB2163234A
Application number: GB08519970A
Authority: GB
Inventors: Jonathan David Philby
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1984-08-13
Filing date: 1985-08-08
Publication date: 1986-02-19
Also published as: GB2163234B; KR860001940A; US4655983A; EP0173499A1; GB8519970D0; JPS6187949A; GB8420545D0

Description

1 GB 2 163 234A 1

SPECIFICATION

Improvements in or relating to piston rings and their manufacture The invention relates to piston rings for internal combustion engines and to methods for their 5 manufacture.

The purpose of a piston ring of an internal combustion engine is to span the gap between the piston in which the ring is mounted and the associated cylinder or liner in order, during piston reciprocation, to prevent combustion gases passing between the piston and the cylinder and/or to control the thickness of the oil film on the associated cylinder or liner. In its simplest form, 10 piston ring are of generally rectangular cross-section with the longer sides extending radially.

This shape can be quickly and easily produced by a variety of well known methods.

However, benefits have been shown to arise from the use of shaped piston rings. For example, it can be of benefit to provide one or two radially outwardly projecting rails on a piston ring, where the ring is controlling the thickness of the oil film on the associated cylinder or liner. 15 Further, it has been found beneficial to provide a positive radially outward force acting on the ring in order to urge it towards the associated cylinder or liner and for this purpose annular springs have been provided acting on the radially inner surfaces of piston rings. For this purpose, it has been proposed to provide an annular recess extending around the piston ring in order to provide positive location of the spring on the piston ring.

These more complex shapes are more difficult to manufacture than the simple ring of rectangular cross-section. Many of the known techniques cannot be used. The most common method of producing such rings is by a moulding operation; for example, a sintering and moulding operation, where the piston ring is of metal, or a hot pressing technique where the ring is of a thermosetting plastics material or an injection moulding process, where the ring is of 25 a thermoplastic. However, moulding has the disadvantage that certain shapes can only be produced using complex equipment. For example, where re-entrant surfaces are required, it is necessary to use collapsible cores and this adds to the time, expense and cost of producing a piston ring. Such re-entrants may, for example, be found in the gaps between a pair of outwardly projecting rails or in a recess for a spring.

According to a first aspect of the invention, there is provided a piston ring for an internal combustion engine and formed by upper and lower annular parts having contacting surfaces lying in respective planes normal to the axis of the piston ring.

The two parts of the piston can be simple in shape and so can readily be formed by a moulding process. They can be such, however, that when they are placed together a piston ring 35 of compix shape is produced.

According to a second aspect of the invention, there is provided a method of manufacturing a piston ring according to the first aspect of the invention and comprising forming the upper and lower annular parts separately and then placing said annular parts together to form said piston ring.

The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a first form of piston ring formed by upper and lower annular parts manufactured by an injection moulding process, Figure 2 is a plan view of one annular part of a piston ring formed by upper and lower such 45 parts, and showing a locating peg and recess, Figure 3 is a partial view of the ends of the annular part shown in Fig. 2, Figure 4 is a partial side elevation of a third form of piston ring from upper and lower parts showing the upper part offset relatively to the lower part, and Figure 5 is a partial elevation of a fourth form of piston ring formed from upper and lower parts and including slots of two different kinds extending through the piston ring.

Referring first to Fig. 1, the piston ring is formed of a tough crystalline thermoplastic material or an alloy thereof. An example of such a tough crystalline thermoplastic material is polyether etheretherketone. This is a tough crystalline thermoplastic aromatic polyetherketone containing the repeating unit - - 0 -CY- 0 60 and having an inherent viscosity of 0.7. The polyetheretherketone may be made by the polycondensation of hydroquinone and a 4-4'- dihalobenzophenone (a proportion of which is 44'-diflourobenzophenone) and an alkaline metal carbonate or bicarbonate, as described in European Patent Publication No. 0 001 879. The polyetheretherketone may be unreinforced or 65 2 GB2163234A may be reinforced with carbon fibres which may be randomly arranged or may be orientated to extend, for example around the piston ring. In addition, bronze, graphite or polytetrafluoroethylene may be added to the polyetheretherketone either together or separately. For example, an alloy of the kind disclosed in British Patent Application No. 84,06547 may be used.

The piston ring is formed by upper and lower annular parts 1 Oa, 1 Ob which have the same configuration and include a surface 12 lying in a plane normal to the axis thereof. One of said parts is inverted relative to the other of said parts so that these surfaces 12 are in contact. Each part 1 Oa, 1 Ob includes an outward projection 13 of generally converging trapezoidal crosssection and disposed symmetrically about a median plane of the part normal to the axis thereof.

Each part 1 Oa, 1 Ob also includes a concavely curved inner surface 14 whose maximum depth is10 at the associated contacting surface 12.

Thus, when one annular part is inverted relative to the other, and the two surfaces 12 are placed together, as shown in Fig. 1, the two projections form two annular oil control rails 13 on the finished piston ring with a re-entrant channel 15 between them. The two inner curve surfaces 14 form an annular recess 16 for receipt of an annular coil spring for urging the piston 15 ring outwardly.

There is a gap (not shown) in each part 1 Oa, 1 Ob and the gaps are in or substantially in register.

The two parts 1 Oa, 1 Ob are formed by injection moulding. Since neither part has, in itself, any re-entrant portions, the injection moulding process can be performed quickly and rapidly 20 without using collapsing dies. The re-entrant portions 15, 16 are only formed when the two parts 1 Oa, 1 Ob are placed together to form the complete piston ring. Thus a piston ring of complex shape can be formed cheaply and quickly.

The two parts 1 Oa, 1 Ob may, as shown, be unconnected to allow relative movement therebetween. Alternatively, as shown in Figs. 2 and 3, each part 1 Oa, 1 Ob may be provided 25 with a peg 17 and a recess 18 adjacent the free ends thereof. Thus, when one part is inverted relative to the other, the peg 17 on one part engages in the recess 18 on the other part, in order to prevent relative angular movement between the parts.

The pegs 17 and the recesses 18 need not be symmetrically disposed about the gap; they may be angularly displaced relative to the gap, as shown in Fig. 2, so that when the two parts 30 are placed together, the upper ring 1 Oa is angularly offset relative to the lower ring 1 Ob. This is shown in Fig. 4.

It is a requirement in many piston rings, that slots or holes be provided in the ring to allow the drainage of oil through the ring. The piston ring method described above can be readily adapted to provide such a feature. As shown in Fig. 5, each annular part can be provided with 35 one or more recesses 19 extending across the radial width of the associated part and in register with the recess or recesses 19 of the other part, when the two parts 1 Oa, 1 Ob are placed together. These recesses can form a slot of circular cross-section or a slot of oval cross-section, both forms being shown in Fig. 5. Thus, the co-operating recesses provide the required holes or slots extending radially through the piston ring.

It will be appreciated that the benefits of a two-part construction to piston rings are not confined to those piston rings having re-entrant portions. It may be found easier and cheaper to manufacture various other configurations of piston rings in two parts rather than in one.

In addition, materials other than thermoplastics may be used. For example, thermosetting plastics may be used in a hot pressing process. Further, metals may be used with the parts of 45 the piston ring being formed by a sintering process in which a metal powder is sintered to shape in a suitable die.

Claims

1. A piston ring for an internal combustion engine and formed by upper and lower annular parts having contacting surfaces lying in respect planes normal to the axis of the piston ring.

2. A piston ring according to claim 1, wherein each annular part is formed without re entrants, but is so shaped that the two parts together form at least one re-entrant extending circumferentially around a radially outer surface of the piston ring.

3. A piston ring according to claim 2, wherein each annular part includes an annular 55 projection extending radially outwardly therefrom, to provide the piston ring with two oil control rails with said re-entrant therebetween.

4. A piston ring according to any one of claims 1 to 3, wherein each annular part is formed with a radially inner surface, said radially inner surfaces being complementarily curved to form tdgether a concave recess around the piston ring for the receipt of an annular spring.

5. A piston ring according to any one of claims 1 to 4, wherein the upper and lower annular parts are symmetrical about a plane normal to the axis of the piston ring and including said contacting surfaces.

6. A piston ring according to any one of claims 1 to 5, wherein the upper annular part is angularly offset relatively to the lower annular part.

3 GB2163234A 3

7. A piston ring according to any one of claims 1 to 6, characterised in that the upper and lower annular parts are constrained against relative angular movement.

8. A piston ring according to claim 7, wherein at least one slot is provided on one of said annular parts and at least one projection is provided on the other said annular parts, the at least one slot and projection co-operating to prevent relative angular movement between said annular 5 parts.

9. A piston according to claim 7, wherein the upper and lower annular parts are fixed together at said contacting surfaces.

10. A piston according to claim 9, wherein the fixing is by a mechanical interlock or by a bond such as an adhesive bond or a welded bond.

11. A piston ring according to any one of claims 1 to 10, wherein each contacting surface is provided with at least one recess therein, each recess extending across the radial width of the associated annular part and being in register with the at least one recess of the other annular part to form at least one slot extending through the piston ring.

12. A piston ring for an internal combustion engine substantially as hereinbefore described 15 with reference to the accompanying drawings.

13. A method of manufacturing a piston ring according to any one of claims 1 to 12 and comprising forming the upper and lower annular parts separately and then placing said annular parts together to form said piston ring.

14. A method according to claim 13, wherein the parts are formed by a moulding process. 20

15. A method according to claim 14, wherein the moulding process includes the use of a mould having no re-entrant portions but shaped such that, the two annular parts, when forming said piston ring, define at least one re-entrant extending circumferentially around the piston ring.

16. A method according to claim 14 or claim 15, an din which the piston ring is of metal, the moulding process comprising a sintering process.

17. A method according to claim 13 and in which the piston ring is of a plastic material, the moulding process being either a hot pressing or injection moulding process.

18. A method according to one of claims 13 to 17, and in which the annular parts are symmetrical about a plane normal to the piston axis and including said contacting surfaces, the method comprising forming two annular parts having a common configuration including a surface lying in a plane normal to the axis thereof and the inverting one of said parts relative to the other so that said surfaces are in contact to form the piston ring.

19. A method of manufacture of a piston ring substantially as hereinbefore described with reference to the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 8818935. 1986, 4235 Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained- i