PISTON AND PISTON ASSEMBLIES

Abstract: A piston (10) is assembled with its correct piston rings (12) by the piston manufacturer before dispatch to an engine manufacturer or repairer. This is achieved by use of a piston ring retainer (14, 20, 22, 23, 29, 32, 37) which holds the rings flush with the piston surface and which is such as to allow the assembly to be packaged in a container not substantially different in size from the piston. The assembly can then be removed from the container by the manufacturer or repairer and be inserted into a cylinder bore of an engine with the rings correctly arranged.

Description: PTSTON AND PISTON ASSEMBLIES The invention relates to pistons of the kind having at least one piston ring groove and a piston ring in the or each groove. It has, heretofore, been common practice to package the rings separately from the piston and to assemble the piston and rings only when the piston is about to be inserted into a cylinder bore of an engine by an engine rebuilder or by an engine manufacturer. In general, this assembly is achieved by expanding the or each ring over the piston by opening a gap provided in such rings, then, where there are two or more rings, locating them relatively to one another so that their gaps are not in axial alignment, then selecting a ring compression tool to compress the ring or rings into the associated groove or grooves so that the external diameter does not project beyond the adjacent piston surface and then inserting the piston and ring or rings into the cylinder bore at the same time releasing the ring compression tool. Before assembly, both the ring or rings and the piston are protected, by individual packaging, from damage, by, for example, contact with other metal objects or picking up dirt or dust. However, after the assembly of the piston rings in the manner described above significant damage can be caused both to the piston and to the rings. Damage can occur in the actual unpacking or in the expansion of the rings to pass them over the piston and into the grooves. Unless the ring compression tool is properly applied, the rings can project from the grooves and so damage the cylinder bore as they are inserted. In addition, the rings must be selected by the repairer or manufacturer so that they are the right size for the piston and the grooves, so that they are the right way up, so that they are of the right material and so that the gaps in the rings, where two or more are provided, are not in axial alignment with one another. This may not be a problem where highly skilled personnel are assembling pistons and rings, but may be a considerable problem where less skilled personnel are being used, particularly in the do-it-yourself market. There is also the disadvantage that the assembly of pistons and rings by the engine repairer or manufacturer in the way described above, can take a considerable time. This can increase the cost of engine manufacture or repair. According to the first aspect of the invention, there is provided an assembly of the kind comprising a piston having at least one piston ring groove, a piston ring in the or each groove, characterised in that there is a piston ring retainer holding the piston ring or rings so compressed that they are flush with the piston surface to allow insertion of the piston rings into a cylinder, the piston ring retainer being such as to allow the assembly to be subsequently packed in a container not substantially greater in size than the size of the piston and then to be removed from the container and the piston and piston ring or rings inserted into a cylinder. According to a second aspect of the invention, there is provided a method of packaging a piston and piston ring assembly characterised by the steps of placing a piston ring or rings into a respective piston ring groove or grooves of a piston, retaining the or each piston ring in the grooves so that the piston is flush with the adjacent piston surface, and then packaging the piston and piston ring assembly in a container not OMPI Yλ ~ substantially larger in size than the size of the piston. According to a third aspect of the invention, there is provided a method of inserting a piston and a piston ring or rings into a cylinder bore of an internal combustion engine, the method being characterised by the steps of taking an assembly according to the first aspect of the invention or prepared by a method according to the second aspect of the invention, positioning it over the cylinder bore, inserting the piston into the cylinder bore, by the application of pressure to the crown of the piston, and then removing the piston ring retainer towards the end of said insertion. 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 perspective view, partially cut away, of a first form of assembly of piston, piston rings and a piston ring retainer, Figure 2 is a perspective view of part of an alternative form of the piston ring retainer of Figure Figure 3 is a perspective view, partially cut away, of a second form of piston ring retainer, formed in two parts. Figure 4 shows the parts of the piston ring retainer of Figure 3 before (the left-hand side) and after (right- hand side) assembly, Figure 5 shows an inner part of the piston ring retainer of Figures 4 and 5, Figure 6 shows a perspective view of an assembly of a piston and a third form of piston ring retainer, Figure 7 shows a fourth form of piston ring retainer, and Figure 8 shows a fifth form of piston ring retainer. Referring first to Figure 1, a piston 10 (shown in chain dotted line) comprises three axially spaced piston ring grooves 11. Each groove 11 is fitted with the correct piston ring 12 for that groove (e.g. an oil control ring or a scraper ring or a combined oil control and scraper ring) ; the rings 12 being of the correct material, positioned the correct way up and having their gaps out of axial alignment. It will be appreciated that although three piston rings 12 and grooves 11 are shown in Figure 1, one, two, four or more piston rings and grooves may be provided as required. The piston also includes a gudgeon pin bore 13. A piston ring retainer 14 is placed over the crown end of the piston to hold the piston rings 12 compressed in their grooves 11 so that they lie flush with the surrounding piston surface. The piston ring retainer 14 is formed from a plastics material and has an annular body 15 whose inner surface 16 contacts the piston rings 12 to hold them in the correct position. The piston ring retainer 14 is formed with an inwardly extending flange 17 which contacts the crown 18 of the piston. The piston ring retainer 14 of Figure 1 is applied around the piston 10 by use of a closing tool (not shown) . As will be seen, the piston ring retainer 14 can carry any suitable wording 19. Referring next to Figure 2, the piston ring retainer 20 shown in this Figure is generally the same as that shown in Figure 1, except that the interior surface of the retainer 20 is formed with a plurality of angularly spaced axially extending projections 21 which contact the piston rings to hold them correctly positioned. This retainer 20 is placed over an associated piston and piston rings in the same way as the retainer 14 described above with reference to Figure 1. Referring next to Figures 3, 4, and 5, a second form of piston ring retainer 22 comprises an inner piston ring contacting part 23 and an outer compressing part 24. The inner part is shown in Figure 5, and comprises an annular plastics member with an axial slit. The exterior surface 25 of this inner part is frusto- conical (see also Figure 4) with the narrower diameter at the upper end. The interior surface 20 of the inner part is generally right cylindrical. The gap 27 in the inner part 23 allows it to be expanded and placed over the piston rings but its resilience is such that the rings 12 are not compressed by the inner part 23 alone. The inner part 23 may be used on pistons having a variety of diameters since the presence of the slit allows such variations to be accommodated. The outer part 24 is of metal and is generally frusto- conical in shape, in correspondence with the shape of the exterior surface 25 of the inner part. The cone angle may be 5°. The axial length of the outer part 24 is substantially the same as that of the inner part 23. A radially inwardly directed flange 28 is provided around the smaller diameter end of the outer part 24. As shown in Figure 4, when the inner part 23 (shown stippled in full line in this position) is placed around the piston rings 12, the diameter of its upper end is just less than the diameter of the lower end of the outer part 24. This allows the outer part 24 to be slipped over the inner part 23 and pushed downwardly to compress the inner part 23 (shown in Figure 4 in chain-dotted line and cross-hatched in this position) so forcing the piston rings into the piston ring grooves 11 so that they are at least flush with the piston surface. Movement of the outer part 24 terminates when the flange 28 contacts the crown 18. Referring next to Figure 6, the third form of retainer 29 comprises a continuous member which forms two opposed arcuate sections 30 whose ends are interconnected by connecting parts 31 which can be bent or crimped. The retainer 29 is placed over the piston rings 11 with the connecting parts 31 undeformed, and these parts are then deformed to tighten the sections 30 around the piston rings, so holding them correctly positioned. Referring next to Figure 7, the fourth form of piston ring retainer 32 comprises a thin metal band 33 having a tongue 34 formed at one end and a slotted key 35 at the other. The band 33 is placed around the piston rings in the piston and the tongue 34 inserted through the slot in the key 35. The key 35 is then turned to tighten the band so compressing the piston rings. The band 33 may be provided with angularly spaced lugs 36 for engagement with a cylinder block when the piston is inserted into a cylinder bore, in a manner to be OMPI described below. Referring finally to Figure 8, the fifth form of piston ring retainer 37 may be formed by a band 38 of a plastics material of suitable axial length formed around its circumference with a rack 39 which passes through a ratchet-containing aperture 40 which allows the band only to be tightened so that it cannot then be relaxed. The band 38 is placed loosely around the piston rings in their associated grooves and the band is then tightened. In any of the embodiments described above with reference to the drawings, the lower edge of the retainer may be provided with a formation or formations, such as a bevel, for guiding the retainer over the piston ring or rings, as the sleeve is engaged with the piston, to compress the piston ring or rings. In a further embodiment (not shown) , a sheet of material may be placed over the crown of the piston and then crimped or otherwise deformed down over the piston rings to hold them in the compressed position. The sheet may be of aluminium or a metal reinforced plastics material or any other suitable material. In all the embodiments described above with reference to the drawings, the assembly is formed by the piston and piston ring manufacturer. The completed assembly is then packaged and this can be done cheaply and economically in a container not substantially different in size from the piston, because all the piston ring retainers described above with reference to the drawings are compactly arranged close to the surface of the piston. The pistons and piston ring assemblies are thus supplied complete to the engine manufacturer or repairer. In all the embodiments described above with reference to the drawings, the piston and piston rings are inserted into a cylinder bore of an associated engine in the following way. The assembly is initially unpacked. The lower end of the skirt of the piston is located in the cylinder bore. The piston is next pushed downwardly by pressure on the crown of the piston. Continued downward movement causes the lower edges of the piston ring retainers to contact the block in which the cylinder is formed. This is facilitated by the lugs 36 in the Figure 7 embodiment. Further movement causes the retainer to be gradually pushed- off the piston, and since the retainer has substantially the same diameter as the cylinder bore, the rings will remain compressed and pass readily into the cylinder bore without damaging the cylinder bore or the cylinder block in which the bore is formed. The retainer may then be re-used. This is a particular possibility with the retainer 22 of Figures 3, 4 and 5 because there is no permanent deformation involved in applying the retainer 22 to the piston and piston rings. In addition to the embodiments described above with reference to the drawings, it is possible to fix the piston rings in their compressed position by use of an adhesive which is dispersed when the engine commences operation. For example, it may disperse on the application of heat or pressure or by contact with engine fluid such as oil or petrol vapour. It will be appreciated that all the embodiments of the invention described above with reference to the drawings have the advantage that the piston rings are correctly assembled before they are inserted into the cylinder by an engine manufacturer or a repairer. This means that the rings can be arranged with their gaps properly out of axial alignment, and that the rings can be assembled in the correct order and be of the correct type. There is no problem of an untrained operator assembling and prelocating the rings and so there is less chance of any damage or mis-assembly. The manufacturer's or repairer's assembly time is reduced because the piston rings do not have to be fitted by the repairer of manufacturer. 15PM08.2

Claims: CLAIMS 1. An assembly of the kind comprising a piston (10) having at least one piston ring groove (11) , a piston ring in the or each groove, characterised in that there is a piston ring retainer (14, 20, 23, 24, 29, 32, 32) holding the piston ring or rings (12) so compressed that they are flush with the piston surface to allow insertion of the piston and rings into a cylinder, the piston ring retainer being such as to allow the assembly to be subsequently packed in a container not substantially greater in size than the size of the piston and then to be removed from the container and the piston and piston ring or rings inserted into a cylinder. 2. An assembly according to claim 1, characterised in that the piston ring retainer comprises a generally annular sleeve (14, 20) extending around the part of the piston in which the piston ring groove or grooves (11) are formed and contacting the piston ring or rings (12) to compress said piston ring or rings into the piston ring grooves. 3. An assembly according to claim 2, characterised in that the sleeve (20) contacts the piston ring or rings only at a number of spaced locations (21) around the periphery thereof. 4. An assembly according to claim 2 or claim 3, characterised in that the sleeve has a lower end thereof provided with a formation or formations for guiding the sleeve over the piston ring or rings, as the sleeve is engaged with the piston, to compress the piston ring or rings. 5. An assembly according to any one of claims 2 to 4, characterised in that the sleeve (14, 22) has at one end a closure (17, 24) which extends at least partially over the surface of the crown. 6. An assembly according to claim 5, characterised in that the closure (17, 24) is formed with an aperture (18) to allow the piston (10) to be inserted into a cylinder by pressure applied to the crown, with the sleeve (14, 22), during said insertion, contacting the cylinder block to disengage the sleeve from the piston on continued insertion of the piston. 7. An assembly according to claim 1, characterised in OMPI that the piston ring retainer is formed in two parts (23, 24), a radially expandable first part (23) which contacts the piston ring or rings (11) and a second part (24) which fits over the first part to compress the first part (23) radially inwardly to hold the piston ring or rings in position. 8. An assembly according to claim 7, characterised in that the first part (23) is generally annular with an axially extending slit (27) and has a frusto-conical outer surface with a lesser diameter at the crown end of the piston and the second part (24) is annular and inelastic and has a correspondingly frusto-conical interior surface to allow engagement of the two parts to compress the piston rings. 9. An assembly according to claim 1, characterised in that piston ring retainer is formed by a band (29, 37) of adjustable diameter which is locked at a required diameter to hold the piston ring or rings in position. 10. An assembly according to claim 1, characterised in that the piston ring retainer comprises one or more arcuate segments (30) whose adjacent ends are connected by a circumferential (31) part which is deformed by CMPI clipping or pinching so that the arcuate segment or segments have a diameter required to compress the piston ring or rings. 11. An assembly according to claim 1, characterised in that the piston ring retainer is formed by a plastics material shrunk or shrunk-wrapped over the piston and piston ring or rings. 12. An assembly according to claim 1, characterised in that the piston ring retainer is an adhesive which disperses on the application thereto of heat or pressure or on contact with engine fluid such as oil or petrol vapour so that the piston rings are released on first operation of the engine. 13. A method packaging a piston and piston ring assembly characterised by the steps of placing a piston ring or rings (12) into a respective piston ring groove or grooves (11) of a piston (10) , retaining the or each piston ring in the grooves so that the piston is flush with the adjacent piston surface, and then packaging the piston and piston ring assembly in a container not substantially larger in size than the size of the piston. 14. A method of inserting a piston and a piston ring or rings into a cylinder bore of an internal combustion engine, the method being characterised by the steps of taking an assembly according to any one of claims 1 to 12 or prepared by a method according to claim 16, positioning it over the cylinder bore, inserting the piston into the cylinder bore, by the application of pressure to the crown of the piston, and then removing the piston ring retainer towards the end of said insertion. 15PM08.3

Inventors: COLLYEAR JOHN GOWEN, GRAHAM NEIL ANTHONY, COLLYEAR, JOHN, GOWEN, GRAHAM, NEIL, ANTHONY
Applicants: AE PLC
Application year: 1984
Main classification: B65D59
IPC codes: B25B27, F16J9