GB1588515A

GB1588515A - Pistons

Info

Publication number: GB1588515A
Application number: GB3649376A
Authority: GB
Original assignee: Associated Engineering Ltd
Current assignee: Associated Engineering Ltd
Priority date: 1976-09-02
Filing date: 1976-09-02
Publication date: 1981-04-23
Also published as: JPS5331013A; JPS611617B2; DE2736815C2; DE2736815A1; FR2363705B1; FR2363705A1; IT1082621B

Description

(54) PISTONS (71) We, ASSOCIATED ENGINEERING LIMITED, a British Company of Ince House, 60, Kenilworth Road, Leamington Spa CV32 6JZ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to pistons such as are used in combustion engines, and more particularly but not exclusively in diesel engines.

According to the invention, a piston comprises a metal body part including a skirt portion and a pair of gudgeon pin bosses, the piston also including a crown, at least the central part of which is formed by a ceramic insert, and a metal annular insert-retaining part surrounding the periphery of the ceramic insert which retains the ceramic insert in position and secures it to the metal body part of the piston such that said insert is prestressed in axial compression.

The annular insert-retaining part may comprise a tubular annular portion surrounding the periphery of the ceramic insert and provided with a retaining flange directed towards the longitudinal axis of the piston and overlapping the insert. The tubular portion may form part of the metal body part, i.e. it may be cast integrally with the metal body part or may comprise an insert cast in the body part, and the retaining flange may comprise a ring welded to, or in screw-thread engagement with, the tubular portion.

Alternatively, the tubular portion may be in screw-thread engagement with the body part, and the retaining flange may comprise a ring formed integrally with, or welded to, the tubular portion.

The tubular portion of the annular retaining part may be made wholly of cast iron or aluminium alloy, or of aluminium alloy or other light metal alloy with a cast-in insert of cast iron, to which the retaining flange or ring is secured.

The tubular portion, preferably, forms at least a part of the piston ring carrier of the piston.

Preferably the insert is prestressed by giving the retaining flange or ring an interference fit with the ceramic insert, which may for example be a silicon nitride insert, when it is attached to the tubular portion, or when the tubular portion is attached to the body part of the piston, thus pre-stressing exists when when the piston is at room or ambient temperature.

A number of embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure ]. is a longitudinal section of a first embodiment of piston taken in a plane coincident with the gudgeon pin axis; Figure 2 is a section on the line 11-Il of Figure 1; Figure 3 is a longitudinal section of a second embodiment of piston, on the gudgeon pin axis; Figure 4 is a section on the line IV-IV of Figure 3; Figure 5 is a composite view of a third embodiment of piston showing a right-hand half-section on the gudgeon pin axis, and a left-hand half-section on the thrust axis; Figure 6 is a composite view, sectioned as Figure 5, of a fourth embodiment of piston; Figure 7 is a composite view, sectioned as Figure 5, of a modification of Figure 5;; Figures 8 and 9 are fragmentary crosssections, on an enlarged scale, of modified versions of the pistons shown in Figures 1 and 3 respectively; Figure 10 is a fragmentary cross-section, on an enlarged scale, of a modified version of the piston shown in Figure 3; Figure 11 is a composite view, sectioned as Figure 5, of another embodiment; Figure 12 is a composite view, the righthand half being a section on the line XI-XI of Figure 11, and the left-hand half being an underneath plan view in the direction of the arrow XII in Figure 11; Figure 13 is a composite view, sectioned as Figure 5, of a modification of Figure 11; Figure 14 is a composite view, sectioned as Figure 5, of yet another embodiment; Figure 15 is a composite view, sectioned as Figure 5, of yet another embodiment; and Figure 16 is a composite view, the righthand half being a section on the line XVI--XVI of Figure 15, and the left-hand half being an underneath plan view in the direction of the arrow XVII in Figure 15.

The piston shown in Figures 1 and 2 includes a metal body part comprising a skirt 10 formed integrally with a pair of gudgeon pin bosses 11 from an aluminium alloy. The body part has at its upper end an integral transverse wall having a peripherally stepped, planar upper undercrown surface 12. The central part of the crown of the piston is formed by a ceramic insert, for example a silicon nitride insert 13, formed with a combustion bowl 14 and an annular rebate 15 round the periphery of its upper surface. The insert is circular in transverse cross-section, and is concentric with the body part of the piston. The silicon nitride insert 13 is secured to the aluminium alloy body part by means of an innular insert-retaining part comprising a tubular annular portion 16 which has an inwardly directed annular flange 17 engaging with the rebate 15.The tubular portion 16 is internally screwthreaded at its lower end 1 6a to engage with an externally screw-threaded annular rebate 12a in the periphery of the upper undercrown surface 12 of the body part.

The tubular portion 16 forms an upward continuation of the skirt 10, and is formed with annular grooves intended to receive and locate the conventional piston rings (not shown). The tubular portion 16 thus constitutes a ring carrier portion of the piston.

On assembly of the piston, the tubular ring carrier portion 16 is screwed onto the body part to the extent necessary to cause a slight interference fit between the flange 17 and the rebate 15 of the silicon nitride insert 13, so as to place the silicon nitride insert axially in compression between the flange 17 and the planar seating formed by the planar undercrown surface 12. The ring carrier portion 16 may be formed initially with castellations 18 (shown in broken lines) to facilitate screwing it to the body part, the castellations being machined away after assembly.

The ring carrier portion is locked against rotation by means of a grub-screw 19.

The ring carrier portion 16, and the flange 17 which in this embodiment is formed integrally with the ring carrier portion, are preferably made of cast iron or steel.

Referring now to Figures 3 and 4, the piston body part has a skirt 20 and gudgeon pin bosses 21 similar to those of Figures 1 and 2, and a silicon nitride insert 23 formed with a combustion bowl 24 and abutting a flat upper undercrown surface 22 of the transverse wall of the body part. The silicon nitride insert also has a rebate 25 around the circumference of its upper surface, but in this embodiment the tubular portion of the annular insert-retaining part, namely the ring carrier portion 26, forms an integral part, of the body part. The silicon nitride insert 23 is retained by an inwardly directed annular flange in the form of an externally screw-threaded retaining ring 27 which engages with an internal screw thread at the upper end of the annular ring carrier portion 26, and also with the rebate 25 in the insert 23.The internal periphery of the ring carrier portion 26 and the external periphery of the insert 23 are stepped to form cooperating frusto-conical shoulders 261 and 23t respectively. Thus, the insert is housed in a generally cylindrical stepped recess afforded by the annular ring carrier portion 26 and the upper undercrown surface 22.

The retaining ring 27 is received into the ring carrier portion 26 so as to create an interference fit with the insert 23 to place the insert in compression axially of the piston. The initial axial dimension of the retaining ring 27 may be significantly longer than its final axial dimension and provided with castellations 28 (shown in broken lines) to facilitate the screwing-in of the ring, and, after assembly, may be parted off flush with the top surface of the piston in a lathe or similar machine tool.

Referring now to Figure 5, the piston body part has an aluminium alloy skirt 30 and integral gudgeon pin bosses 31. The centre of the transverse undercrown portion or wall. 32 of the piston body has an aperture 32a to receive a spigot 33a on the silicon nitride insert 33. The insert 33 in this embodiment has a stepped generally frustoconical seating, and more particularly the cooperating surfaces of the undercrown wall 32 and insert 33 have an annular inner zone radiating from the spigot which is of frustoconical configuration, and is bounded by a stepped outer annular zone. The piston has a cast-in iron ring carrier member 36 in which the uppermost piston ring groove is formed, the remaining grooves being formed in the aluminium alloy portion of the body part. The ring carrier member projects beyond the alloy portion of the body part at the crown end of the piston. The insert 33 is formed with a circumferential rebate 35 in its upper surface, and is housed in a circular-section stepped housing defined by the tubular portion of the insert-retaining part, which, in this embodiment is formed partly by the upper end of the ring carrier member 36, and partly by the previously mentioned stepped outer annular zone which is formed in the alloy portion of the body part in which the ring carrier member is embedded. A retaining ring 37 engages with the rebate 35, the ring being located within the ring carrier member 36 and joined thereto by an axially directed weld such that the insert is pre-stressed in axial compression.

A similar construction to that shown in Figure 5 may have the retaining ring 37 screwed to ring carrier member 36.

The piston shown in Figure 6 differs from that shown in Figure 5 in that the retaining ring 37 is superimposed on the castin ring carrier member 36 and is joined thereto by a radially directed weld, although the retaining ring could alternatively be welded or screwed within the ring carrier member 36 as described with reference to Figure 5. Additionally, the central spigot of the insert 33 is omitted, and the iron ring carrier member 36 is longer, forms the entire tubular portion of the insert-retaining part including the stepped outer annular zone, and is formed with three piston ring grooves instead of a single groove.

Figure 7 shows a modified version of the piston of Figure 5 in which the ring carrier member 36 is of intermediate length, forms the entire tubular portion of the insertretaining part, and is formed with two piston ring grooves. In addition, the undercrown surface of the insert 33 radiating from the spingot 33a is frusto-conical throughout, and the cooperating frusto-conical undercrown surface of the body part is provided partly by the alloy portion of the body part and partly by the ring carrier member 36, i.e. the stepped outer annular zone of Figure 5 is omitted. The retaining ring 37 is shown as being welded into the upper end of the ring carrier member 36, although it could be screwed thereinto or be superimposed on and welded to the ring carrier member as shown in Figure 6.

In preferred arrangements, a spring washer of the "Belleville" type, which is basically in the form of a frusto-cone, may be inserted in an axial gap between the peripheral rebate in the silicon nitride insert 13, 23 or 33 and the retaining flange or ring 17, 27 or 37 of any of the previously described embodiments to provide an axial load, so as further to help to retain the insert in position when, in operation, the metal of the piston expands on heating. Such a washer is shown at 17a in Figure 8 and 27a in Figure 9, which illustrate modified versions of the pistons shown in Figures 1 and 3 respectively. An equivalent result may al ternatively be achieved by inserting a similar spring washer between the cooperating undercrown surfaces of the insert and body part to urge the insert against the retaining flange or ring.A comparable spring, for example a corrugated spring making line contact parallel to the piston axis, may be provided in a radial gap formed between the insert and insert-retaining part, for example the tubular or ring carrier portion, in any of the previous embodiments. Such a washer is shown at 27b in Figure 10, which illustrates a modified version of the piston shown in Figure 3. Another suitable form of spring for either position is a resilient woven metal mat.

Referring to Figures 11 and 12, the piston shown has a body part, made of iron, provided with two skirt segments 40 each extending over approximately 800 of the pistons circumference and joined to gudgeon pin bosses 41 solely by webs 42a. The ring carrier portion 46 is integral with the gudgeon pin bosses 41, and a frusto-conical undercrown transverse wall or portion 42 is connected to the gudgeon pin bosses 41 through the ring carrier portion 46 and through webs 42b. The undercrown portion 42 has a central aperture which receives a spigot 43a on a silicon nitride insert 43 formed with a combustion bowl 44. The insert is concentric with the piston and is secured by means of a superimposed retaining ring 47 welded to the upper end of the ring carrier portion, although it may alternatively be secured to the ring carrier portion in any of the other ways previously described.The retaining ring lacts to place the insert axially in compression.

Figure 13 shows a modified version of the piston of Figure 11 in which the surfaces of the insert 43 and transverse wall or portion 42 of the body part are of similar form to those of Figure 6.

Figure 14 shows another form of aluminium alloy piston, somewhat similar to that shown in Figure 3, but in which the cooperating undercrown surfaces of the insert 53 and of the transverse wall or portion 52 of the body part, are of part spherical form, curved about a single radius centred on the piston axis. In addition, the insert 53 is retained in the generally cylindrical housing afforded by the transverse undercrown portion 52 and the ring carrier portion 56, by means of a retaining ring 57 which is superimposed upon and welded to the upper end of the ring carrier portion 56, similar to the ring 47 in Figure 11.

Figures 15 and 16 show yet another form of iron piston, somewhat similar to that of Figure 13, the body part having two skirt segments 60 joined to gudgeon pin bosses 61 solely by webs 62a.

The ring carrier portion 66 is integral with the gudgeon pin bosses 61, and a curved or part-spherical transverse under cr ) n wall or portion 62 is connected to the gudgeon pin bosses 61 through the ring carrier portion 66 and webs 62b. The silicon nitride insert 63 is received in the substantially cylindrical housing by the ring carrier portion 66 and the transverse undercrown portion 62, and is secured by a retaining ring 67 engaging in a rebate 65 in the insert 63 and superimposed on and welded to the upper end of the ring carrier portion so as to place the insert in axial compression.

The retaining rings in Figures 13 to 16 may alternatively be secured to their associated ring carrier portions in any of the ways described previously.

It will be understood that various modifications may be made without departing from the scope of the present invention as defined in the appended claims. For example, the inserts may be made from ceramic materials other than silicon nitride, such as silicon carbide, sialons, glass ceramics or other ceramics, provided that they possess the properties of high resistance to thermal shock and the ability to operate at high temperatures.

Our copending divisional application 80 06330 (Serial No. 1588516) describes and claims a piston wherein the ceramic insert is a shrink fit in the metal annular insertretaining part.

WHAT WE CLAIM IS:- 1. A piston comprising a metal body part including a skirt portion and a pair of gudgeon pin bosses, the piston lalsd including a crown, at least the central part of which is formed by a ceramic insert, and a metal annular insert-retaining part surrounding the periphery of the ceramic insert which retains the ceramic insert in position and secures it to the metal body part of the piston such that said insert is pre-stressed in axial compression.

2. A piston as claimed in claim 1, -wherein the annular insert-retaining part comprises a tubular portion surrounding the periphery of the insert, and wherein the in sert 55 concentric with the longitudinal axis of the piston.

3. A piston as claimed in claim 2, wherein the tubular portion forms an integral part of the body part.

4. A piston as claimed in claim 2, wherein the tubular portion is cast in the body part.

5. A piston as claimed in claim 2, wherein the tubular portion and body part are formed with interengaging screw threads by which the tubular portion is secured to the body part.

6. A piston as claimed in any of claims 2 to 5, wherein the tubular portion is a continuation of the skirt, and forms at least a part of the piston ring-cairying portion of the piston.

7. A piston as claimed in any of claims 2 to 6, wherein the tubular portion includes an annular retaining flange which is directed towards the longitudinal axis of the piston and overlaps the insert, said flange serving to place the insert axially in compression.

8. A piston as claimed in claim 7, wherein the flange is integral with the tubu lar portion.

9. A piston as claimed in claim 7, wherein the flange comprises a separate re taining ring secured to the tubular portion.

10. A piston as claimed in claim 9, wherein the retaining ring and tubular por tion are provided with interengaging screw threads by which the retaining ring is secured to the tubular portion.

11. A piston as claimed in claim 9, wherein the retaining ring is bonded to the tubular portion.

12. A piston as claimed in any of claims 7 to 11, wherein the flange engages in a peripheral rebate in the crown surface of the insert with an interference fit between the flange and the rebate.

13. A piston as claimed in any preced ing claim, including resilient means operable to accommodate differential thermal expan sion between the insert and the annular in sert-retaining part in the axial direction of the piston.

14. A piston as claimed in any preced ing claim, including resilient means oper able to accommodate differential thermal expansion between the insert and the an nular insert-retaining part in a direction transverse to the longitudinal axis of the piston.

15. A piston as claimed in any preced ing claim, wherein the insert is located on a generally planar seating of the body part.

16. A piston as claimed in any of claims 1 to 14, wherein the insert is located on a generally frusto-conical seating of the body part.

17. A piston as claimed in any of claims 1 to 14, wherein the insert is located on a generally part-spherical or otherwise curved seating of the body part.

18. A piston as claimed in claim 16 or 17, wherein the insert is provided with an axial spigot engaged in an axial aperture in the seating of the body part.

19. A piston as claimed in lany of claims 15 to 18, wherein the seating of the body part is peripherally stepped.

20. A piston as claimed in any preced ing claim, wherein the ceramic insert is formed from silicon nitride or other high temperature-resistant and high thermal shock-resistant ceramic.

21. A piston as claimed body any preced ing claim, wherein the body part and/or annular insert-retaining part are formed from a cast iron.

22. A piston as claimed in any of claims 1 to 20, wherein at least the body

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. nitride insert 63 is received in the substantially cylindrical housing by the ring carrier portion 66 and the transverse undercrown portion 62, and is secured by a retaining ring 67 engaging in a rebate 65 in the insert 63 and superimposed on and welded to the upper end of the ring carrier portion so as to place the insert in axial compression. The retaining rings in Figures 13 to 16 may alternatively be secured to their associated ring carrier portions in any of the ways described previously. It will be understood that various modifications may be made without departing from the scope of the present invention as defined in the appended claims. For example, the inserts may be made from ceramic materials other than silicon nitride, such as silicon carbide, sialons, glass ceramics or other ceramics, provided that they possess the properties of high resistance to thermal shock and the ability to operate at high temperatures. Our copending divisional application 80 06330 (Serial No. 1588516) describes and claims a piston wherein the ceramic insert is a shrink fit in the metal annular insertretaining part. WHAT WE CLAIM IS:-

1. A piston comprising a metal body part including a skirt portion and a pair of gudgeon pin bosses, the piston lalsd including a crown, at least the central part of which is formed by a ceramic insert, and a metal annular insert-retaining part surrounding the periphery of the ceramic insert which retains the ceramic insert in position and secures it to the metal body part of the piston such that said insert is pre-stressed in axial compression.

22. A piston as claimed in any of claims 1 to 20, wherein at least the body

part is fonned from an aluminium alloy or other light metal alloy.

23. Pistons constructed substantially as hereinbefore described with reference to Figs. 1 and 2, or Figs. 3 and 4, or Fig. 5, or Fig. 6, or Fig. 7, or Fig. 8, or Fig. 9, or Fig. 10, or Figs. 11 and 12, or Fig. 13, or Fig. 14, or Figs. 15 and 16 of the accompanying drawings.