GB2129523A

GB2129523A - Composite pistons

Info

Publication number: GB2129523A
Application number: GB08327969A
Authority: GB
Inventors: Edward John Murray
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1982-10-20
Filing date: 1983-10-19
Publication date: 1984-05-16
Also published as: GB8327969D0

Abstract

A composite piston has a metal crown 10,22, and a plastics skirt 11,33 separated by a heat-insulating barrier. In one aspect, the skirt is of polyetheretherketone or polyetherketone or a plastics alloy of an aromatic polyetherketone and a polyarylene sulphide or a polypharahydroxy benzoic acid or a silicon modified polyester. The barrier may be provided by articulating the crown and skirt together, Figure 1, or by the provision of a chamber 28 beneath the crown. <IMAGE>

Description

SPECIFICATION Composite Pistons The invention relates to composite pistons for internal combustion engines in which the crown is of metal and the skirt is of a plastics material.

According to the invention, there is provided a piston for an internal combustion engine, comprising a crown of a metallic material and a skirt separated from the crown by a heat-insulating barrier, the skirt having an outer skirt surface of a plastics material.

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 side elevation, partially in section, of a first form of piston for an internal combustion engine; Figure 2 is a similar view to Figure 1, but showing a modification of the first form of piston, Figure 3 is a cross-section through a second form of piston for an internal combustion engine, and Figure 4 is a similar view to Figure 3, but showing a modification of the second form of piston.

Referring first to Figure 1, the piston is suitable for a petrol or a diesel engine and comprises a crown 10 and a skirt 11. The crown 10 is formed from a metallic material, such as aluminium or aluminium alloy, by casting, for example by squeeze casting, and may include such features as a combustion bowl. Where the piston is for a diesel engine, the combustion bowl may be reinforced around the entrance thereof by a reinforcing material introduced during casting. The crown 10 has three piston ring grooves 12 formed therein which may be reinforced by wear-resistant material also introduced into the crown during casting. Two tapering gudgeon pin bosses 13 depend from the undersurface, radially inwardly of the outer curved surface of the crown 10. The bosses 13 have registering gudgeon pin bores 14for receipt of a gudgeon pin 15.In an alternative embodiment, not shown, the bosses 13 may be parallel.

The skirt 11 is formed from a plastics material so as to provide a plastics skirt surface for contacting an associated cylinder or liner. A pair of diametrically opposed gudgeon pin bores 16 are provided and skirt 11 fits over the gudgeon pin bosses 13 of the crown 10. In this position the skirt gudgeon pin bores 16 are in register with the crown gudgeon pin bores 14so that the gudgeon pin 15 passes through all four bores 14, to connect the crown 10 to the skirt 11 in an articulated fashion. Circlips 17 hold the gudgeon pin 15 in position. Thus, there is a heat-insulating barrier, formed by the air gap between the crown 10 and the skirt 11, which limits the passage of heat from the crown 10 to the skirt 11.

This reduces the temperature of the skirt 11 and allows the skirt to be made either of high temperature resistant plastics materials such as polyetheretherketone, polyetherketone, a plastics alloy of an aromatic polyether ketone and a polyarylene sulphide (as described in British Patent Application No.8131821), a polyparahydroxy benzoic acid or a silicon modified polyester or a polyetherimide or a polyimide, any other, less temperature resistant, plastics material which has the necessary strength and the ability to form an effective lubricant film, such as polytetrafluoroethylene or nylon. The plastics material may be reinforced with glass, metal, organic or metal oxide fibres or wires. The skirt 11 may be formed by extrusion or injection moulding or by pressing and curing a plastics powder or by spraying or any other suitable plastics forming process.

Where the plastics alloy is used, it may be formed of polyetherketone and polyphenylene suphide in ratio, by weight, of between 95:5 and 5:95. This alloy has a fatigue strength suitable for a piston skirt and also has the property of forming an effective lubricant film on its surface so that, in use, the skirt 11 is adequately lubricated. The alloy may be produced by solvent blending, using benzyl benzoate as the solvent, or by melt blending. This is as described in British Patent Application No.8131821.

Referring next to Figure 2, parts common to this Figure and to Figure 1 will be given the same reference numerals and will not be described in detail. In the modification of Figure 2, the skirt 11 is formed in two parts: a support 1 1a of a metallic material such as aluminium or aluminium alloy surrounded by a generally cylindrical sleeve 11b of the plastics materials described above with reference to Figure 1. The sleeve 1 1b thus forms the skirt surface. The skirt gudgeon pin bores 16 pass through the support 1 lea and the sleeve 1 1b, with the circlip 17 engaging in the metallic support 11a.

The sleeve 11b may be formed by any of the methods described above with reference to Figure 1.

This modified embodiment has the benefits that the metallic support 1 1a gives rigidity to the skirt 11 as well as helping to conduct heat downwardly from the gudgeon pin 15. In addition, the metallic support 1 1a is better able than the plastics material of the sleeve 1 1b to bear the loads imposed, in use, by the gudgeon pin 15.

Referring next to Figure 3, the second form of piston is suitable for use in diesel engines and comprises a crown 20 and a skirt 21. The crown 20 includes a top plate 22 of a ferrous material, such as stainless steel, and formed with a combustion bowl 23. A U-section ring 24, also of a ferrous material such as stainless steel, is welded or brazed around the periphery of the undersurface of the top plate 22.

The undersurface of the ring 24 is, in turn, welded or brazed or diffusion bonded to a lower member 25 having the same area as the top plate 22 and being of a metallic material such as aluminium or aluminium alloy. A stack of annular discs or washers 27, roughened by oxidation (to reduce the transfer of heat therebetween), are placed between the plate 22 and the lower member 25, beneath the combustion bowl 23.

There is thus formed a main sealed chamber 28 between the plate 22 and the lower member 25 and a subsidiary sealed chamber 29 between the ring 24 and the top plate 22. These chambers may contain air or a vacuum and/or (not shown) an insulating material. Thus there is provided a heat-insulation barrier between the top plate 22 and the lower member 25.

The lower member 25, forms in one piece, both the remainder of the crown and a support portion 32 of the skirt 21. This support portion 32 carries, on its outer surface, a sleeve 33 of any of the plastics materials described above with reference to Figure 1, whether reinforced or non-reinforced and,-due to the presence of the insulating chambers 28,29, whether high temperature resistant or not. The sleeve 33 forms the skirt surface and is produced in any of the ways described above with reference to Figure 1.

The lower member 25 is formed with three piston ring grooves 30 and gudgeon pin bores 31, which latter also pass through the sleeve 33.

Referring next to Figure 4, parts common to this Figure and to Figure 3 will be given the same reference numerals and will not be described in detail. In this modification, an additional heatinsulating barrier 26 is provided between the chambers 28, 29 and the lower members 25. This may take the form of a porous metal material such as a knotted metal wire or tape or a three dimensional mesh or the material sold under the trade name RETIMET carried at the upper end of the lower member 25. This may be achieved by placing the porous metal material in a mould and then casting the lower member therearound, with the metal penetrating the porous metal material only partially.

The casting process may be a squeeze casting process.

In this case, the undersurface of the ring 24 will again be welded, brazed or diffusion bonded to the porous metal material.

It will be appreciated that the plastics material of the skirts described above with reference to the drawings need not be the same material throughout.

For example, the crown-end of the skirt may be made of a more heat-resistant plastics material and the end of the skirt remote from the crown of a less heat-resistant plastics material.

The skirt need not extend all around the piston, it may only extend partially around or may be formed in segments. The plastics material and the support, where provided, can be bonded together and this bonding can be by any suitable process. The bonding may be performed with a metal support in the form of a sheet followed by bending of the composite so formed to produce the skirt. The skirt can be attached to the crown in any one of the ways described above with reference to the drawings.

Alternatively, the crown and support(s) may be formed in one-piece and the plastics material bonded to the support(s) in a subsequent operation.

Claims

1. A piston for an internal combustion engine, comprising a crown of a metallic material and a skirt separated from the crown by a heat-insulating barrier, the skirt having an outer surface of a plastics material.

2. A piston according to Claim 1, wherein the plastics material is a polyetheretherketone or a polyetherketone or a plastics alloy of an aromatic polyetherketone and a polyarylene sulphide or a polyparahydroxy benzoic acid or a silicon modified polyester or a polyetherimide or a polyimide.

3. A piston according to Claim 1 or Claim 2, wherein the plastics material is reinforced with glass or metal or organic or metal oxide fibres orwires.

4. A piston according to any one of Claims 1 to 3, wherein the skirt comprises a metallic support carrying, on an outer surface thereof, a plastics member forming the plastics skirt surface.

5. A piston according to Claim 4, wherein the plastics member is formed as a generally cylindrical sleeve extending around the outer surface of the metallic support.

6. A piston according to any one of Claims 1 to 5, wherein the piston is an articulated piston with the crown being formed separately from the skirt and the crown and skirt having corresponding gudgeon pin bores to allow connection therebetween by a gudgeon pin, to form an air gap therebetween which provides said heat-insulating barrier.

7. A piston according to any one of Claims 1 to 6, wherein the air-insulating barrier comprises a sealed chamber provided in the crown.

8. A piston according to Claim 7, wherein the chamber contains a vacuum.

9. A piston according to Claim 7 or Claim 8, wherein the crown comprises a top plate connected to the remainder of the crown around the periphery thereof but spaced from the remainder of the crown inwardly of said periphery to form said chamber.

10. A piston according to any one of Claims 7 to 9, wherein a further insulating barrier is provided by a layer of insulating material extending over that surface of the remainder of the crown which bounds the chamber.

11. A piston according to Claim 10, wherein the insulating material comprises a porous metal material included in the crown.

12. A piston for an internal combustion engine, substantially as hereinbefore described with reference to Figure 1 or to Figure 1 as modified by Figure 2, or to Figure 3 or to Figure 3 as modified by figure 4 of the accompanying drawings.