GB2060130A

GB2060130A - Piston

Info

Publication number: GB2060130A
Application number: GB7912318A
Authority: GB
Original assignee: Massey Ferguson Perkins Ltd
Current assignee: Perkins Engines Group Ltd
Priority date: 1979-04-07
Filing date: 1979-04-07
Publication date: 1981-04-29
Also published as: GB2060130B

Abstract

A piston for an internal combustion engine comprises a cast aluminium alloy body having embedded therein a composite insert 1 comprising a copper alloy combustion chamber lip insert preferably secured to a seat member 2 and located co-axially with the combustion chamber, a piston ring carrier insert 5 located in the circumference of the body, and anchoring means 7 for the lip insert 1 terminating in a portion 8 mechanically keyed and/or metallurgically bonded to the piston body in a region thereof, which at operating temperatures, is at a temperature such that loosening of the anchoring means is prevented, wherein the ring carrier 5 is secured to the anchoring means 7 and the anchoring means 7 is secured to the seat member 2. The lip insert may be directly connected to the ring carrier. Preferably, the seat member 2 and the ring carrier insert 5 are attached to the anchoring means 7 by means of apertured lugs 3, 6 engaging the anchoring means 7. Preferably, the lugs 3, 6 are immovably secured to the anchoring means 7 by clamping between a shoulder on the anchoring means 7 a spacer 12 and an end portion enlarged by deformation at the outer end of the set member 2. The spacer may be omitted. <IMAGE>

Description

SPECIFICATION Piston Having an Insert This invention relates to pistons for internal combustion engines and in particular to inserts incorporated in pistons for internal combustion engines for the purpose of providing armour for combustion chamber bowls and piston ring grooves and to a method of manufacturing such pistons.

It is well known in the piston art to provide inserts respectively for the lip or edge of the combustion chamber bowl and for a piston ring groove, such inserts being of different metal from that of the body of the piston for the purpose of providing resistance to operating conditions tending to produce cracking of the crown and undue wear of the piston ring grooves. Such inserts are often referred to as "armour". The term "lip" is hereinafter intended to include the edge or rim of both re-entrant and non-re-entrant types of combustion chamber bowls formed in the piston.

One difficulty which has beset attempts to provide lip armour is that, due to the arduous service conditions, the inserts become loosened and various ways of anchoring the insert by mechanical keying or metallurgical bonding have been suggested. One proposal was to join the lip insert to the ring carrier insert by limbs and cast the piston body alloy around the inserts.

A further difficulty is that the most suitable material for the lip insert appears to be a copper base alloy and since the body of the piston is an aluminium alloy, there is incompatibility between the insert and piston body due to likely formation of undesirable metallurgical conditions at the interface of the two alloys especially during casting of the piston body. Composite inserts of two or more metals are more expensive and add to the production operations.

Anchoring the lip insert by means of limbs attached to the insert and embedded in the piston body has achieved some success in tests in which the limbs extend into a portion of the body where the temperature in service is sufficiently low, e.g.

1 502C, (that is, creep resistance of the aluminium alloy is sufficiently high) to prevent loosening of the embedded limb and are mechanically keyed and/or metallurgically bonded to the piston body in that portion of the body forming the gudgeon pin boss area. The temperature gradients of pistons are known to those skilled in the piston art.

In the manufacture of pistons, it has been the preferred practice to cast the piston alloy around the lip insert, the insert being provided with either a profile to achieve mechanical keying with the piston alloy or being provided with legs or with connections to the ring carrier insert as the anchoring means, and this has resulted in an undesirable interface between the copper alloy and the aluminium alloy.

The present invention seeks to provide a piston having a copper alloy combustion chamber lip insert of a construction which simplifies assembly and provides a secure anchorage for the lip insert.

According to the present invention, a piston for an internal combustion engine comprises a cast aluminium alloy body having a crown portion and a combustion chamber in the crown and having embedded therein a composite insert comprising a copper alloy combustion chamber lip insert located co-axialiy with the combustion chamber, a piston ring carrier insert located in the circumference of the body, and anchoring means for the lip insert terminating in a portion mechanically keyed and/or metallurgically bonded to the piston body in a region thereof, which at operating temperatures, is at a temperature such that loosening of the anchoring means is prevented, therein the ring carrier is secured to the anchoring means and the anchoring means is secured to the lip insert or to a seat member to which the lip insert is attached.

Preferably, the lip insert and the ring carrier insert are attached to the anchoring means by means of apertured lugs engaging the anchoring means. Preferably, the lugs are immovably secured to the anchoring means by clamping between a shoulder on the anchoring means and an end portion enlarged by deformation.

The ring carrier insert, the anchoring means and the seat member are preferably made from ferrous materials which are resistant to the conditions of service and which will not produce undesirable metallurgical conditions at the interface with the aluminium alloy body. Suitable materials are a cast-iron containing 3% carbon, 14% nickel, 7% copper, and 3% cobalt, or a stainless steel.

The lip insert may be a copper 0.5% beryllium, 2.5% cobalt alloy or a copper, 2.5% nickel, 0.5% silicon alloy, or an aluminium bronze containing 8-10% aluminium.

Preferably the various components of the composite insert are made separately, and after assembly are rigidly secured together.

The ring carrier is conveniently an annular casting provided with lugs on its inner circumference, each lug being adapted to be secured to one of the anchoring means, for example, by means of a hole through which the anchoring means is passed or an open slot which can be deformed to grip the anchoring means.

The anchoring means are preferably stainless steel legs each having an anchoring portion consisting of an end portion of bulbous or other mechanically keying shape. The opposite end portion is preferably adapted to be attached to the seat member or to the lip insert and a shoulder is provided adjacent the said opposite end portion to abut the lug of the ring carrier. The anchoring portion is located in that portion of the piston mentioned above which has sufficient creep resistance to prevent loosening of the insert.

The seat member is preferably initially a ring, but a disc can be used and machined to form a ring after the composite insert has been embedded in the piston body. Preferably, the seat member is a stainless steel weldable to copper alloy, for example, 18/8 stainless steel, and if desired the ring may be provided with a chamfered inner edge prior to incorporation in the composite insert for receiving a lip insert. Lugs can be conveniently incorporated in a cast ring for accommodating anchoring means and are located on the outer circumference. The seat member may be of nickel cast iron when it is intended to secure the copper alloy lip insert thereto by screwing or brazing.

In order to locate the ring carrier at the required spacing from the lip insert and the crown a spacer may be interposed between the lugs of the seat member and the lug of the ring carrier or the lugs may be offset respectively from the seat member or ring carrier. The need for some form of spacing is, of course dictated by the piston design and in certain cases, the ring carrier and seat member or lip insert may be in abutment.

Where it is desired to omit the seat member, the copper alloy lip insert may be provided with lugs, as in the case of the seat member, and the anchoring means secured directly to the lugs of the lip insert.

A preferred manner of securing the anchoring means to the seat member or to the lip insert is by placing the end portion of the anchoring means in a hole in the lug and deforming the end to enlarge it, as in rivetting. Other methods of attachment include screw threading and brazing or welding as appropriate to the materials being used.

In an alternative method of securing the anchoring means to the seat member or the lip insert, the ring carrier insert is attached to the anchoring means and the assembly encast in a piston body, the end portions of the anchoring means adjacent the crown being exposed by machining or by suitable coring techniques, and the preformed seat member or lip insert lugs placed over the end portions and rivetted over as earlier mentioned. A variation of this method is to heat the seat member or lip insert to a hot working temperature, and after locating on the end portions, to deform the seat member or lip insert or the lug so as to grip the anchoring means.A benefit of this method is that the seat member or lip insert can be hot deformed to form a tight fit in the machined or cored-out recess providing access to the anchoring means, and rivetting of the end portion can also be carried out if required.

Both the ring carrier insert and the seat member or lip insert may be assembled on the anchoring means by screw threading, though obviously this increases production costs.

Preferably, the anchoring means are legs of stainless steel rod machined or cold forged to the desired shape with the end portion adjacent the shoulder being firmly fixed, for example, an inference fit, in the hole in the lug of the ring carrier insert. If desired the end portion fitting into the lug of the seat member or the lip insert may be of reduced diameter so producing a shoulder against which lug abuts thus avoiding the necessity for a spacer between the lugs.

Where a seat member is included in the composite insert, the lip insert is secured thereto either before or after casting the piston body around the composite insert. The seat member may with advantage be formed with a 300--450 chamfered surface which mates with a complementary chamfered surface on the lip insert, but chamfers of any angle up to 450 can be welded by a suitable technique.

The use of a seat member and the securing of the lip insert thereto is referred to in detail in our co-pending application.

One method of manufacturing a piston in accordance with the invention comprises, assembling a composite insert by securing a ring carrier insert to the anchoring means, encasting the composite insert in a piston body, exposing end portions of the anchoring means, engaging apertures provided in a seat member or a lip insert on the exposed end portions and securing the end portions in the apertures. The seat member or lip insert can be secured by hot or cold deformation, brazing or welding as before described.

In a variation of the above method, the composite insert is assembled by securing the ring carrier insert to the anchoring means, securing the seat member or the lip insert to the end portion of the anchoring means and encasting the composite insert in a piston body.

When a seat member is incorporated in the composite insert, the method may include the step of securing the lip insert to the seat member.

This may involve exposing the seat member by machining part of the crown of the piston.

The end portions of the anchoring means may be exposed by machining the cast body or by providing cores in the piston mould which prevent piston metal enveloping the end portions. Such cores may also form an aperture for the combustion chamber.

There is some advantage to be derived from the use of a composite insert including the lip insert, which may be either attached directly to anchoring means or attached to a seat member which is directly secured to the anchoring means.

In such a case, fewer operations may be required on the cast body; Preferably the lip insert is secured to the seating surface by a welding operation, for example, friction welding, laser welding, electron beam welding, or resistance welding or by brazing. Where the size of the seat member permits, a screw threaded connection may be made between the seat member and the lip insert, the seating surface in this case being a threaded portion on the inner surface of a ring shaped seat member. In the case of a friction welded joint, the lip insert material may be supplied in the form of a bar or tube which is fed successively to pistons being so welded, the portion welded to the seat member being parted off at the correct angle to weld to the succeeding seat member. The angle of the seating surface to the axis of the seat member is a matter of choice.

Suitable lip insert material includes a copper, 0.5% beryllium, 2.5% cobalt alloy, or "Hidurel" 5 (Trade Mark) a copper 2.5% nickel, 0.5% silicon alloy or aluminium bronze containing 8-10% aluminium.

Where the lip insert is secured to the seat member after the piston body has been case, the combustion chamber may be provided in the crown either before or after the operation to secure the lip insert to the seat member, and in some instances the chamber may be necessary for achieving welding of the lip insert to the seat member by permitting access of a welding device to the appropriate area.

Since the conventional practice of locating piston ring carrier insert in the mould is by pegs in the wall of the mould, the methods herein described can be easily adapted into current practice. The principle difference from current practice lies in the need for accurately locating the legs of the composite insert in the skirt portion of the mould. There are two requirements in this respect. Firstly, correct orientation is essential to ensure that the legs are located in the desired part of the gudgeon pin boss area and to obtain combustion bowl offset where this is required. Secondly, radial location is desirable to ensure that the anchors do not break through the wall of the finished piston skirt.For this purpose means are provided when the composite insert, with or without the lip insert, is placed in the mould, by which the legs are located in predetermined positions in relation to the portion of the mould cavity defining the skirt portion of the piston.

Such means include projections within the mould cavity which engage the legs or projections on the legs which engage the walls of the mould cavity. The latter form of projection may be integral with or affixed to the legs. Another means for location may be apertures or grooves or pegs in the base of the mould cavity in which the ends or projections on the ends of the legs are engaged. The piston ring carrier insert is engaged by pegs in the wall of the mould in the method of the invention in the same way as in current practice, and registers, such as notches on the ring carrier for engagement with the pegs may be provided to ensure correct orientation.

It is also known art to coat the piston ring carrier insert and anchoring means with a bonding metal. One such bonding metal is an aluminium silicon alloy commercially applied by the Alfin process (Trade Mark) and this process or other suitable bonding metal can be applied to the composite insert in the present method.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings of which Figure 1 represents a perspective view of one form of composite insert which includes a seat member; Figure 2 is a cross section on the line A-A of Figure 1; Figure 3 is a cross sectional view of an alternative arrangement to that of Figure 2, omitting the spacer; Figure 4 is a cross sectional view of another arrangement wherein the ring carrier insert and the seat member are in abutment, and Figure 5 is a cross sectional view of a further arrangement in which the seat member is omitted and the copper alloy lip insert is secured directly to the anchoring means.

Referring to the drawings a composite insert 1 comprises an annular seat member 2 made from a ferrous material such as nickel cast iron or stainless steel and having integral lugs 3 diametrically located. A chamfered seating surface 4 is provided on the inner circumference of the seat member 2.

A ring carrier insert 5 is located adjacent the seat member 2 and is formed with integral lugs 6 on the inner circumference. Two stainless steel legs 7 having bulbous ends 8 and a shoulder 9 (Figure 2) pass through a hole 10 in the lug so that the shoulder 9 abuts the lug 6. The ends of the legs 7 are received in a hole 11 in the lug 3 aligned with hole 10 of lug 6. Between the lug 6 and the lug 3 is a tubular spacer 12.

As can best be seen in Figure 2, the hole 11 has a counter sunk portion 13 into which the end 14 is deformed to form a head as in rivetting. The seat member 2, the spacer 12 and the ring carrier insert 5 are thus firmly secured between the shoulder 9 and the head 14. Since the thermal expansion coefficients of the legs 7, seat member 2, spacer 12 and ring carrier insert 5 are similar, loosening of the joint in service does not occur.

To avoid use of the spacer 12, the embodiment shown in Figure 3 may be adopted, in which the lug 3 is offset from the seat member 2 by a distance equal to the length of the spacer 12, and the lug 3 is located in abutment with the lug 6 of the ring carrier insert 5. The leg 7 is passed through aligned holes 10 and 11 to engage the shoulder 9 with the lug 6 and the end of the leg is deformed to form rivet head 15. When case into a piston body, the rivet head 15 is embedded in cast metal.

Another embodiment in which the spacer 12 is absent is shown in Figure 4. The lug 3 is a peripheral extension of the seat member 2, as in the embodiment of Figure 2, and the said lug 3 and the lug 6 of the ring carrier insert 5 are secured in abutment on the end portion of leg 7 between the shoulder 9 and the rivet head 14.

In each of the embodiments described with reference to Figures 1 to 4 the composite insert 1 is embedded in a piston by placing the composite insert 1 in the cavity of a piston mould and casting piston metal around it. The crown of the piston is machined to expose the seating surface 4 of the seat member 2, and if desired, a combustion chamber may be formed in the piston body at the same time. A lip insert 19 with a surface complementary to seating surface 4 is then secured to the seat member 2 by a suitable welding technique.

A modification of the composite insert 1 in which the seat member 2 is absent can be seen in Figure 5. In this case, the copper alloy lip insert 1 6 is provided with a lug 17, and the stainless steel leg 7, by virtue of the shoulder 1 9 and the rivet head 14, clamps the lip insert 16, the stainless steel spacer 12 and the nickel cast iron ring carrier insert 5 firmly together as in the previous embodiments. A variation shown in Figure 5 is the provision of a flange 1 8 on the inner circumference of ring carrier insert 5 instead of a lug for attaching the ring carrier insert to the leg 7.

In the modification shown in Figure 5, the composite insert thus produced is embedded in a piston by encasting as before described with or without metallurgical bonding. The lip insert 1 6 is then located in the crown of the piston and a combustion chamber can then be machined therein.

Claims

1. A piston for an internal combustion engine comprising a cast aluminium alloy body having a crown portion and a combustion chamber in the crown and having embedded therein a composite insert comprising a copper alloy combustion chamber lip insert located co-axially with the combustion chamber, a piston ring carrier insert located in the circumference of the body, and anchoring means for the lip insert terminating in a portion mechanically keyed and/or metallurgically bonded to the piston body in a region thereof, which at operating temperatures, is at a temperature such that loosening of the anchoring means is prevented, wherein the ring carrier is secured to the lip insert or to a seat member to which the lip insert is attached.

2. A piston as claimed in claim 1 in which the anchoring means engages apertures in the lip insert or seat member and the ring carrier insert.

3. A piston as claimed in claim 2 in which the lip insert or seat member and the ring carrier are clamped between a shoulder on the anchoring means and an end portion of the anchoring means.

4. A piston as claimed in claim 3 in which the ring carrier is provided with lugs on its inner circumference with said apertures formed therein.

5. A piston as claimed in claim 3 or 4 in which the lip insert or seat member is provided with lugs with said apertures formed therein.

6. A piston as claimed in claim 5 in which the lugs are offset from the body of the lip insert or seat member so as to space it away from the ring member.

7. A piston as claimed in any one of claims 3 to 5 in which a spacer or spacers are provided between the lip insert or seat member and the ring carrier insert.

8. A piston as claimed in any one of claims 2 to 5 in which a reduced end portion of the anchoring means engages an aperture in the lip insert or seat member, the shoulder on the anchoring means adjacent said reduced end portion abutting the lip insert or seat member.

9. A piston as claimed in any one of claims 2 to 7 in which the anchoring means is secured to the lip insert or seat member by deforming the end of the anchoring means in said apertures in the lip insert or seat member.

10. A piston as claimed in any one of the preceding claims in which the anchoring means are lugs having an anchoring end portion of bulbous or other mechanically keying shape.

11. A method of manufacturing a piston in accordance with claim 1 comprising, assembling a composite insert by securing the ring carrier insert to the anchoring means, encasting the composite insert in a piston body, exposing end portions of the anchoring means, engaging apertures provided in the seat member or a lip insert on the exposed end portions and securing the end portions in the apertures.

12. A method of manufacturing a piston in accordance with claim 1 comprising assembling a composite insert by securing the ring carrier insert to the anchoring means, securing the seat member or the lip insert to the end portion of the anchoring means and encasting the composite insert in a piston body.

13. A method as claimed in claim 12 in which the lip insert is secured to the seat member after casting.

14. A method as claimed in claim 13 in which the lip insert is welded to the seat member.

15. A method as claimed in claim 13 or 14 in which the combustion chamber is formed in the crown of the piston after casting.

1 6. A method as claimed in claim 1 5 in which the lip insert is secured to the seat member after forming the combustion chamber.

1 7. A piston for an internal combustion engine substantially as herein described with reference to Figures 1 and 2 or Figures 3, 4 or 5 of the accompanying drawings.

18. A method of manufacturing a piston for an internal combustion engine substantially as herein described with reference to Figures 1 and 2 or Figures 3, 4 or 5 of the accompanying drawings.