GB2143006A

GB2143006A - Anchoring wear-resisting piston inserts

Info

Publication number: GB2143006A
Application number: GB08326213A
Authority: GB
Inventors: Roger Anthony Day
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1982-10-04
Filing date: 1983-09-30
Publication date: 1985-01-30
Also published as: GB8326213D0; GB2143006B

Abstract

An annular wear-resistant insert suitable for a piston ring groove of an aluminium or aluminium alloy piston of an internal combustion engine has a generally U-shaped axial cross-section (Fig. 7) with the mouth of the U opening outwards and includes an annular part 11 defining a plurality of apertures which can be filled with metal during casting of the piston body to anchor the insert. The insert is particularly suitable for use in a top ring groove which is very close to the piston crown. An alternative structure for part 11 is shown in (Fig. 5). <IMAGE>

Description

SPECIFICATION Pistons, inserts for pistons, and methods of their manufacture The invention relates to aluminium or aluminium alloy pistons for internal combustion engines having a piston ring groove reinforced by an annular insert, to inserts for such pistons and to methods of manufacture of both the pistons and the inserts.

The need to reinforce the piston ring grooves of an aluminium alloy piston with a material substantially more wear-resistant than the aluminium or aluminium alloy is well established. One previous proposal has been the metallurgical bonding and encasting of an annular cast iron insert within the piston, and the machining of a piston ring groove within the insert. Another previous proposal has been the swaging of steel rails into a formed piston ring groove to form side walls of the groove.

According to a first aspect of the invention, there is provided an insert for a piston ring groove of an internal combustion engine piston of aluminium or aluminium alloy, the insert comprising a reinforcing member of generally U-shaped cross-section with the limbs of the member having respective inner and outer annular surfaces, at least one inner surface being for forming a reinforced side wall of the piston ring groove and at least one outer surface carrying an annular connecting member including a plurality of apertures therethrough, through which the material of a body of the piston is to extend to lock the insert to the piston body, the insert being of a material which is more wear-resistant than aluminium or aluminium alloy.

According to a second aspect of the invention, there is provided a piston for an internal combustion engine comprising a body of aluminium or aluminium alloy and at least one piston ring groove formed in the body, said piston ring groove being reinforced by an annular insert according to the first aspect of the invention, at least one inner surface of the insert forming a reinforced sidewall of the piston ring groove and the material of the insert extending through said apertures to lock the insert to the piston body.

According to a third aspect of the invention, there is provided a method of manufacturing a reinforce mentfora piston ring groove of an internal combustion engine piston of aluminium alloy, the method comprising forming a reinforcing member of generally U-shaped cross-section opening outwardly of the member and having inner and outer annular surfaces formed on the limbs of the U-section, and then connecting to at least one of said outer surfaces an annular connecting member including a plurality of apertures extending therethrough.

According to a fourth aspect of the invention, there is provided a method of manufacturing a piston for an internal combustion engine and comprising forming a mould, placing an insert according to the first aspect of the invention or made by the third aspect of the invention in the mould and then filling the mould with molten aluminium or aluminium alloy, so that the molten metal flows around and into the apertures in the connecting member.

The following is a more detailed description of one embodiment of the invention, by way of example, reference being made to the accompanying drawings in which: Figure lisa view of a metal strip for forming a reinforcing member of an insert for a piston for an internal combustion engine, Figure 2 is a view of the formed reinforcing member of the insert, Figure 3 is a section on the line Ill-Ill of Figure 2, Figure 4 is a view of a first form of connecting member for incorporation in the insert, Figure 5 is a second form of connecting member for incorporation in the insert, Figure 6 is a view of the assembled insert, and Figure 7 is a partial cross-section of a piston of an internal combustion engine, showing the insert of Figures 1 to 5 positioned in the piston, Referring first to Figure 6, the insert is formed by an annular reinforcing member 10 of generally U-shaped cross-section and an annular connecting member 11.

Referring next to Figures 1,2 and 3, the reinforcing member 10 is formed from a strip 12 of a ferrous material, such as any suitable sheet or a carbitic steel such as that designated EM31. The strip is formed with a plurality of spaced holes 13 extending along the centre line of the strip.

The strip is then folded along two lines parallel to the edges of the strip but spaced inwardly of the edges of the strip to form the strip into a reinforcing member of U-shaped cross-section (see Figure 3).

The member 10 is thus formed with two limbs 14, 15 interconnected by a base 26 of the U, along which the holes 13 are arranged. The limbs have respective inner surfaces 14a, 15a and outer surfaces 14b, 15b and converge towards the base 26.

The U-shaped strip 12 is then formed into an annulus of required diameter.

Referring next to Figure 4, the first form of connecting member 11 is formed from a thin strip of mild steel, for example a low carbon mild steel. The strip is folded to form a plurality of interconnected U-shaped sections 16 lying in planes parallel to one another and having interconnections 17 between alternately opposite pairs of adjacent ends of successive limbs.

The coiled strip is then bent and formed into a circle of a diameter intermediate the inner and outer diameters of the reinforcing member 10. The strip is so arranged that the bases of the U section 16 lie on a conical surface which has the same cone angle as the cone angle of the limbs 14, 15 of the reinforcing member 10.

Two such connecting members 11 are prepared.

Strips having a similar serpentine configuration to the connecting member 11 are sometimes used as expanders for piston rings in piston ring grooves of pistons for internal combustion engines. Accordingly, a length of such an expander may be used to form the connecting members 11,so obviating the need to bend a strip into serpentine shape.

As an alternative, the second form of connecting member 1 1a as shown in Figure 5 may be used. This member is formed from a thin strip of mild steel, for example, a low carbon mild steel. The strip is corrugated to form a plurality of inverted U-shaped sections 16a connected together by interconnections 17a between the ends of adjacent links of the U-shaped sections. The corrugated strip is then bent and formed into a circle of a diameter intermediate the inner and out diameters of the reinforcing member 10. The strip is so arranged that the interconnections 17a lie on a surface which has the same cone angle as the cone angle ofthe limbs 14, 15 of the reinforcing member 10. Two such connecting members 11a are provided.

The connecting members 11, 1 is are next joined to the reinforcing member 10. This is done by placing a connecting member 11, 1 la on each outer surface 14b, 1 5b of the limbs 14, 15 of the U-shaped member and then joining the interconnections 17, 17a to the associated surface. This may be done by any suitable welding technique such as spot welding or projection welding or by brazing or by diffusion bonding methods. As seen in Figure 16, the connecting members 11, 1 lea are preferably so arranged that there is an interconnection 17, 17a spanning the join between the abutting ends of the reinforcing member 10. This gives the assembled insert a degree of rigidity, while also retaining a degree of flexibility.

The reinforcement is then placed in the requisite position in a casting die for casting a piston around the reinforcement. The insert may be placed in the die (as shown in Figure 7)so that it forms a top ring groove close to a crown of the piston (a 'headland' groove). However. it may, if required, be positioned to form a conventional top ring groove or second ring groove.

The reinforcement may be placed on a crown plate in a crown-down squeeze casting die or may be carried on carrier pegs of a conventional crown-up gravity casting die. A molten casting alloy which may, for example, be an aluminium-silicon-coppernickel-magnesium alloy known as Lo-Ex, is then poured into the die. The molten casting metal penetrates through the holes 13 and also in and around the apertures provided by the U-sections 16, 16a. If the casting process is a squeeze casting process, the pressure applied during solidification of the molten metal ensures that there is dense aluminium alloy around all parts of the reinforcement. In addition, the squeeze casting operation will ensure that any tendency towards solidification shrinkage is obviated.It will be appreciated, however, that an adequate flow of molten metal around the reinforcement may be achieved by a gravity casting process.

After casting, the piston body 18 (see Figure 6) and the reinforcement are removed from the die. Because there is a complete mechanical lock between the reinforcement and the piston body 18, the piston can be given full conventional heat treatment, quenching and precipitation.

Next, the piston is machined. This involves finish machining the exterior surface of the piston and also machining away the cast aluminium alloy between the limbs 14,15, ofthe inserttoform a piston ring groove. The dimensions of the reinforcing member 10 may be such that its radial depth is significantly greater than the required radial depth of the piston ring groove 19, so that the base of the groove is formed by cast piston metal. This provides additional keying of the insert to the piston body 18. During this machining process, material may be removed from the ends of the limbs 14, 15 and from the inner surfaces 14a, 15a.

The insert described above with reference to the drawings is particularly suitable for reinforcing a piston ring groove which is very close to the crown of the piston. Such grooves receives a so-called 'headland' ring which has a groove-engaging portion of keystone cross-section (a generally trapezoidal section narrowing towards the base of the groove).

The formation of such grooves in cast-in inserts has the problem that, because the insert engages the piston body on two sides only, it is difficult to ensure that such an insert is securely bonded to the piston body. Even of a satisfactory bond is established, the bond is prone to damage which may cause the insert to loosen and damage the engine.

The swaging of steel rails into a preformed groove at such a position cannot be satisfactorily achieved because there is insufficient axial thickness of the material of the piston body between the upper side wall of the groove and the crown. The thickness of material will not withstand the swaging loads or the operating temperatures encountered.

In contrast to these proposals, the insert described above with reference to the drawings can be located very close to the crown of the piston. There is a complete mechanicalinterlock between the insert and the piston body and this is established before the finish machining of the piston. The piston material surrounds the insert on three sides and also penetrates into the base of the reinforcing member 10.

It will be appreciated, however, that the insert described to reinforce either a conventional top ring groove of a piston or any other such ring groove.

This insert is particularly suitable for reinforcing the second ring groove when the top ring groove is to be formed in an insert cast and bonded to the piston.

This is because no metallurgical bond has to be established between the piston metal and the insert described above with reference to the drawings.

There is thus no restriction on the time interval which may elapse between the time when the insert is placed in the mould and the time when casting commences, in contrast to the requirements for establishing certain metallurgical bonds.

It will be appreciated that the limbs 14,15 may be parallel to receive a conventionally shaped ring of rectangular cross-section. It will also be appreciated that the depth of the reinforcing member 10 may be the same as the depth of the piston ring groove 19 so that the base 26 of the member 10 forms the base of the groove 19. The reinforcing member 10 and the connecting member 11, 1 1a may be formed in one piece.

It will also be appreciated that the join between the ends of the reinforcing member 10 is filled with aluminium or aluminium alloy so that there is no possibility of cylinder gases leaking around any gap between these ends.

Claims

1. An insert for a piston ring groove of an internal combustion engine piston of aluminium or aluminium alloy, the insert comprising a reinforcing member of generally U-shaped cross-section with the limbs of the member having respective inner and outer annular surfaces, at least one inner surface being for forming a reinforced side wall of the piston ring groove and at least one outer surface carrying an annular connecting member including a plurality of apertures therethrough, through which the material of a body of the piston is to extend to lock the insert to the piston body, the insert being of a material which is more wear-resistant than aluminium or aluminium alloy.

2. An insert according to claim 1, wherein the connecting member is formed separately from the reinforcing member and is subsequently connected thereto by a welding or a brazing or a diffusion bonding technique.

3. An insert according to claim 2, wherein the connecting member is formed by a plurality of interconnected U-shaped sections each lying in a respective plane including the piston axis.

4. An insert according to claim 3, wherein the connecting member is formed from a single strip of material with the U-shaped sections being interconnected between alternately opposite pairs of adjacent ends of successive limbs.

5. An insert according to claim 2, wherein the connecting member is formed from a single strip of material which is corrugated with the peak of each corrugation connection to the reinforcing member to form said apertures.

6. An insert according to any one of claims 1 to 5, wherein there are two connecting members, one on each outer surface of the reinforcing member.

7. An insert according to any one of claims 1 to 6, wherein the or each connecting member is made from a low carbon mild steel.

8. An insert for a piston ring groove of an internal combustion engine piston substantially as hereinbefore described with reference to Figures 1 to 4 and 6 orto Figure 5 of the accompanying drawings.

9. A piston for an internal combustion engine comprising a body of aluminium or aluminium alloy and at least one piston ring groove formed in the body, said piston ring groove being reinforced by an annular insert according to any one of claims 1 to 8, at least one inner surface of the insert forming a reinforced side wall of the piston ring groove and the material of the insert extending through said aperturves to lockthe inserttothe piston body.

10. A piston according to claim 9, wherein both inner surfaces of the reinforcing member form respective side walls of the piston ring groove.

11. A piston according to claim 10, wherein the inner surfaces of the reinforcing member are parallel or converge towards the radially inner ends of the piston ring grooves.

12. A piston according to claim 10 or claim 11, wherein the base of the reinforcing member, connecting the limbs, is provided with a plurality of apertures angularly spaced therearound, the material of the piston body extending through said hole and filling the inner end of the reinforcing member to form a base of the piston ring groove.

13. A piston according to any one of claims 10 to 12, wherein the reinforcing member is made of sheet steel or of a carbitic steel.

14. A piston for an internal combustion engine substantially as herein before described with reference to Figure 7 of the accompanying drawings.

15. A method of manufacturing a reinforcement for a piston ring groove of an internal combustion engine piston of aluminium or aluminium alloy, the method comprising forming a reinforcing member of a generally U-shaped cross-section opening outwardly of the member and having inner and outer annular surfaces formed on the limbs of the Usection, an annular connecting member including a plurality of apertures extending therethrough.

16. A method according to claim 15, wherein the step of forming the reinforcing member comprises forming a base of the U-shaped portion, which connects the limbs, 'A,ith a plurality of apertures angularly spaced therearound.

17. A method according to claim 15 or claim 16, wherein the reinforcing member is formed from a a flat strip of a ferrous material, the strip being sent to form the U-shape and then being bent into an annulus.

18. A method according to any one of claims 15 to 17, wherein the step of joining the annular connecting member to the reinforcing member comprises a welding or a brazing or a diffusion bonding technique.

19. A method according to any one of claims 15 to 18 and including forming the annular connecting member from a single strip of metal bent to provide a plurality of angularly spaced U-shaped sections lying in respective planes including the axis of the insert, with the sections being interconnected between alternately opposite pairs of adjacent ends of successive limbs.

20. A method according to claim 19, wherein the joint between the connecting member and the reinforcing member is between the interconnections and said reinforcing member.

21. A method according to any one of claims 15 to 18 and including forming the annular connecting member from a single strip of metal bent to form corrugations.

22. A method according to any one of claims 15 to 20 and wherein the reinforcing member is formed from a single piece of material bent into an annulus and having two adjacent ends, the step of joining the connecting member thereto then comprising joining a part of the connecting member across the abutting ends of the reinforcing member to hold said ends together.

23. A method according to any one of claims 15 to 22, wherein the method comprises joining the annular connecting members to both the outer surfaces of the reinforcing member.

24. A method of manufacturing a piston ring groove reinforcement substantially as hereinbefore substantially as hereinbefore described with reference to the accompanying drawings.

25. A method of manufacturing a piston for an internal combustion engine and comprising forming a mould, placing in the mould an insert according to any one of claims 1 to 8 or made by the method of any one of claims 15 to 24 and then filling the mould with molten aluminium or aluminium alloy, so that the molten metal flows around and into the apertures in the connecting member.

26. A method according to claim 25 and including the application of pressure to the solidifying metal by a squeeze casting technique.

27. A method according to claim 25 or 26 and further comprising removing the cast piston from the mould and machining a piston ring groove in the piston body so that at least one side wall of the piston ring groove is formed by at least a portion of one inner surface of the reinforcing member.

28. A method according to claim 27, wherein the machining step comprises machining the grove so that the radial depth of the groove is less than the radial depth of the reinforcing member, so that the base of the groove is formed by the aluminium alloy of the body.

29. A method according to claim 27 or 28, wherein the machining step comprises machining away at least some of the side wall-forming inner surface of the reinforcing member and/or at least some of the end of the limb on whit said side wall-forming surface is provided.

30. A method according to any one of claims 27 to 29 and further comprising, before the machining step, the heat treatment, quenching and precipitation of the cast piston.

31. A method of manufacturing a piston substantially as hereinbefore described with reference to the accompanying drawings.