GB2196094A

GB2196094A - Pistons

Info

Publication number: GB2196094A
Application number: GB08721583A
Authority: GB
Inventors: Michael Geoffrey Donnison; Robert Alan Wordsworth; Michael Ledsham Price Rhodes
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1986-09-18
Filing date: 1987-09-14
Publication date: 1988-04-20
Anticipated expiration: 2007-09-14
Also published as: GB8622538D0; GB2196094B; US4838149A; EP0261726B1; GB8721583D0; EP0261726A2; DE3769257D1; EP0261726A3

Description

GB2196094A 1 SPECIFICATION The iron-based or nickel-based alloy annular

portion may also include a hollow, sealed cav Pistons ity within the portion. The cavity may extend around the whole annular portion and itself be The present invention relates to pistons and 70 annular in form. The cavity may be of varying to methods of manufacture of such pistons cross-section around its length. The cavity for internal combustion engines and particu- may be formed by the joining together of two larly to pistons having insulating crowns to component parts to form the annular portion.

reduce the heat loss from the engine combus- The ceramic insert may also include a com- tion processes. 75 bustion bowl in, for example, diesel applica- US 4,553,472 of common ownership here- tions. The bowl may have any desired confi- with describes pistons having crowns which guration and be positioned symmetrically or are heat insulated from the remainder of the asymmetrical with regard to either the piston piston. Heat insulation is primarily accom- crown or the insert.

plished by the incorporation of sealed air gaps 80 The ceramic insert may itself comprise two between the crown and the remainder of the or more different ceramics. The main body of piston. Embodiments are shown where the the insert may comprise silicon nitride, for crown combustion bowl surface is formed of example, whilst the surfaces thereof may be expensive nickel based superalloys to with- coated with partially stabilised zirconia, for stand the increased temperatures which heat 85 example.

insulation generates. However, it is known Energy beam welding may be by either elec- that erosion and corrosion effects on the tron beam or laser beam.

metal bowl surface can occur in diesel applica- In order that the present invention may be tions in the region of impingement of the fuel more fully understood examples will now be jets. For this reason the use of ceramic ma- 90 described by way of illustration only with ref terials having inherently better resistance to erence to the accompanying drawings of such effects is desirable for forming the com- which:

bustion bowl. Ceramic materials in most in- Figures 1 to 5 show a section through five stances also have more desirable heat insulat- alternative embodiments of pistons according ing properties than metals. It has been pro- 95 to the present invention; posed to use ceramics for combustion bowls Figures 6 and 6A show a sixth alternative before. Indeed in US 4,553,472 the proposal embodiment, Figure 6A being a view of a sec is made. The problem has always been, how- tion through plane AA of Figure 6.

ever, in securing the bowl insert in position Referring now to Figure 1 and where similar for long term endurance which in an automo- 100 features are denoted by common reference tive diesel truck engine, for example, may numerals. A diesel engine piston is shown need to be of the order of 500,000 miles. generally at 10. The piston 10 comprises a Methods using various graded brazes for se- crown component 11 and a skirt component curing ceramics are very expensive and require 12. The crown component 11 is formed by very precise process control. Fitting of the in- 105 an annular ring portion 13 made from an iron sert into the aluminium alloy of the piston has or nickel based alloy. Shrink-fitted to the ring not proved successful due to the high coeffici- portion 13 is a ceramic insert 14 having a ent of expansion of the aluminium alloy rela- combustion bowl 15 formed therein. The cera tive to the ceramic which either allows the mic material of the insert 14 may, for insert to loosen or necessitates an unnaccep- 110 example, comprise silicon nitride or partially table degree of interference. However, fitting stabilised zironia (PSZ) or a combination of ceramic to iron or nickel-base alloys has thereof. The skirt component 12 comprises proved unexpectedly successful. the normal gudgeon pin bores 16, bosses 17 According to the present invention a piston and piston ring grooves 18. Formed in the for an internal combustion engine comprises a 115 upper planar surface 19 of the skirt compo crown component and a skirt component nent 12 are depressions 20 and 21. Depres wherein the crown component consists of an sion 20 is annular in form. The lower end of iron-based or nickel-based alloy annular porthe annular ring portion 13 has a radially thick tion having fitted directly therein a ceramic in- ened portion 22 to which is joined by means sert, the crown component being joined to the 120 of an electron beam or laser weld 23 an an skirt component by an annular composite lami- nular, laminated bimetallic joining member 24.

nated member of steel and aluminium alloy the The member 24 comprises a steel layer 25 steel of the laminated member being energy and an aluminium alloy layer 26 which have beam welded to the annular portion of the been joined together at the interface 27 by a crown. component and the aluminium alloy of 125 pressure welding technique such as roll bond the laminated member being energy beam ing. The crown component 11 is then joined welded to the skirt component there being to the upper surface 19 of the skirt compo after welding a sealed, hollow, annular cham- nent 12 by a second annular electron beam or ber disposed at the junction between the laser formed weld 28 between the aluminium crown component and the skirt component. 130 alloy of the annular member 24 and the alumi- 2 GB2196094A 2 nium alloy of the skirt 12. Formed at the junc- The offset combustion chamber of Figure 3 tion of the steel 25 of the annular member 24 may, of course, be achieved by means of a and the thickened portion 22 of the annular symmetrical upper annular member 51 and ring 13 is the upper piston ring groove 29. providing a ceramic insert 14 itself having an After welding of the crown component 11 to 70 offset combustion chamber. In a similar man the skirt component 12 the lower face 30 of ner centrally positioned combustion chambers the ceramic insert 14 rests against the upper with respect to the piston crown may be pro face 19. An annular air-gap 31 is formed at duced by employing symmetrical annular mem the junction of the ring portion 13, ceramic bers 50 and 52 and insert 14.

insert 14, upper face 19 and annular joining 75 Figure 4 shows a modification to the em- member 24. The air-gap 31 further signifibodiment of Figure 3 in that the air gaps cantly enhances the heat insulating qualities of 20,21 are replaced by a ceramic disc 60 of the piston and serves to reduce thermally in- particularly low thermal conductivity, for duced stresses at the junction of dissimilar example, PSZ. The disc 60 is located in a materials. 80 recess 61 formed in the upper face 19 of the The ceramic bowl insert may be shrink-fitted skirt component 12.

after the member 13 has been joined to the The disc 60 may alternatively be located in skirt component 12. a corresponding recess in the base of the in- Where the insert 14 comprises two or more sert 14 or may merely be located by interfer- different ceramic materials the second material 85 ence between two substantially flat surfaces.

may be coated on some of the outer surfaces The disc 60 may not necessarily comprise of the main body of the insert. For example, monolithic ceramic but may be formed from a the main body may comprise silicon nitride stee ' 1, ferrous alloy or other metal alloy coated coated with plasma-sprayed PSZ at the re- with PSZ and where the PSZ layer is placed in gions where the insert contacts the annular 90 contact with the lower face of the insert 14.

portion and the piston skirt component. The embodiment of Figure 5 shows a fur- In Figure 2 the annular ring portion 13 fur- ther modification of the embodiment of Figure ther includes a lower base member 40 the 3 in that the lower member 52 of the ring crown component 11 thus incorporating a portion 13 further includes a base member 70 sealed air gap 3 1. The crown component 11 95 and consequent air chamber 71.

is joined to the skirt portion 12 in a similar The hollow ring member 13 of the embodi- manner to that of Figure 1. Formed between ments shown in Figures 3, 4 and 5 further the lower face 41 of the base member 40 improve the heat insulation of the piston and the upper face 19 of the skirt component crown and, therefore, the performance of the 12 is a seated air gap 42 which further en- 100 piston.

hances the insulating properties of the piston- The piston of Figures 6 and 6A again has a The embodiment shown in Figure 3 has an ring member 13 of fabricated construction. It annular ring portion 13 which is itself fabri- comprises two substantially semi-circular cated from two constituent parts. The ring 13 halves 80 and 81 split about the faces 82 comprises an upper eccentric annular member 105 and 83. The ceramic insert 14 is held in the having an eccentric annular channel 51 ring by welding together, preferably by a high therein and a lower annular member 52, which energy beam method, of the two halves on in this case has a shallow eccentric annular the faces 82 and 83. The insert 14 is pro channel 53 therein which co-operates with the vided with a circumferential channel 85 which channel 51 of the upper member 50. The two 110 co-operates with an inturned flange 86 on the members 50 and 52 are joined by an electron halves 80 and 81. This embodiment does not, beam weld 55 to form a hollow, eccentric therefore, rely only upon an interference annular ring 13 having a sealed, eccentric an- shrink-fit between the ring 13 and insert 14.

nular chamber 56 therein. Shrink-fitted into the An additional annular air gap 31 is again ring 13 is a symmetrical ceramic insert 14. 115 formed between the crown and skirt portions.

The crown component 11 so formed is joined This construction is advantageous in that no to the skirt component 12 as described above metal is directly exposed to the combustion with reference to Figure 1. The upper annular gases.

member 50 May be formed by casting, forg- It will be apparent to those skilled in the art ing or machining from a heat and oxidation- 120 that different features of the above embodi resistant iron or nickel-based alloy whilst the ments may be combined in combinations lower member 52 may be made from a less other than strictly as exemplified above.

highly alloyed and cheaper ferrous material.

Claims

Alternatively both members may be produced CLAIMS from titanium alloy, the

electron beam weld 125 1. A piston for an internal combustion en- being optionally replaced by a diffusion gine comprising a crown component and a bond. The use of titanium alloys may be ad- skirt component wherein the crown compo vantageous because of their favourably low nent consists of an iron-based or nickel-based coefficients of thermal expansion and also bealloy annular portion having fitted directly cause of their relatively low density.

130 therein a ceramic insert, the crown component 3 GB2196094A 3 being joined to the skirt component by an annular composite laminated member of steel and aluminium alloy the steel of the laminated member being energy beam welded to the an nular portion of the crown component and the aluminium alloy of the laminated member be ing energy beam welded to the skirt compo nent there being after welding a sealed, hol low, annular chamber disposed at the junction between the crown component and the skirt component.
2. A piston according to Claim 1 wherein the annular portion of the crown component further comprises a lower base member.
3. A piston according to either Claim 1 or Claim 2 wherein the ceramic insert comprises silicon nitride.
4. A piston according to Claim 3 wherein the ceramic insert comprises two or more dif ferent ceramic materials.
5. A piston according to Claim 4 wherein the insert comprises a silicon nitride body at least partially coated with PSZ.
6. A piston according to any one preceding claim wherein the ceramic insert also includes a combustion bowl.
7. A piston according to any one preceding claim wherein the crown component annular portion also includes a hollow, sealed, annular chamber therein.
8. A piston according to Claim 7 wherein the hollow, sealed, annular chamber is non symmetrical.
9. A piston according to any one preceding claim wherein an insulating member is posi tioned between the lower portion of the cera mic insert and the top of the skirt component.
10. A piston according to Claim 9 wherein the insulating member is made of a ceramic material.
11. A piston according to Claim 9 wherein the insulating member comprises a metal coated with a ceramic material.
12. A piston according to Claim 1 wherein the crown annular portion comprises two components which are joined together along faces which substantially lie in a plane which includes the piston axis.
13. A piston substantially as hereinbefore described with reference to the accompanying specification and any one of the Figures from 1 to 6.

Published 1988 at The Patent Office, State House, 66171 High Holborn, London WC1RATP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, KentBR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1187.

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