GB2344149A - Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod - Google Patents

Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod Download PDF

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Publication number
GB2344149A
GB2344149A GB9826051A GB9826051A GB2344149A GB 2344149 A GB2344149 A GB 2344149A GB 9826051 A GB9826051 A GB 9826051A GB 9826051 A GB9826051 A GB 9826051A GB 2344149 A GB2344149 A GB 2344149A
Authority
GB
United Kingdom
Prior art keywords
piston
small end
end portion
connecting rod
casting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9826051A
Other versions
GB9826051D0 (en
Inventor
Nigel Peter Gray
Joseph Hunter
David Charles Wood
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Federal Mogul Technology Ltd
Original Assignee
Federal Mogul Technology Ltd
T&N Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Federal Mogul Technology Ltd, T&N Technology Ltd filed Critical Federal Mogul Technology Ltd
Priority to GB9826051A priority Critical patent/GB2344149A/en
Publication of GB9826051D0 publication Critical patent/GB9826051D0/en
Priority to PCT/GB1999/003896 priority patent/WO2000032336A1/en
Publication of GB2344149A publication Critical patent/GB2344149A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16J—PISTONS; CYLINDERS; SEALINGS
    • F16J1/00—Pistons; Trunk pistons; Plungers
    • F16J1/10—Connection to driving members
    • F16J1/14—Connection to driving members with connecting-rods, i.e. pivotal connections
    • F16J1/22—Connection to driving members with connecting-rods, i.e. pivotal connections with universal joint, e.g. ball-joint
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
    • F05C2201/00—Metals
    • F05C2201/02—Light metals
    • F05C2201/021—Aluminium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
    • F05C2201/00—Metals
    • F05C2201/04—Heavy metals
    • F05C2201/0433—Iron group; Ferrous alloys, e.g. steel
    • F05C2201/0448—Steel

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Shafts, Cranks, Connecting Bars, And Related Bearings (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)

Abstract

A method of manufacturing a piston 12 and a connecting rod 14 assembly comprising mounting a small end portion 16 of a connecting rod 14 in a casting die 30 and casting metal in the die 30 to form the piston, a portion 12c of the piston being cast around the small end portion 16 so that the piston forms a joint with the small end portion 16, the joint having at least one axis about which the piston 12 and the connecting rod 14 can pivot relative to each other. Preferably the small end portion 16 is coated with a material that prevents the metal which forms the piston 12 adhering to the small end portion 16 during the casting process. The coating (27, figure 2) also acts as lubricant during normal operation. Preferably the small end portion 16 is ball-shaped and is disconnecting from the main portion of the connecting rod 14 during casting and reconnected thereafter. Lubrication passages for the joint may also be provided in the piston 12 either during casting or by boring.

Description

MANUFACTURE OF PISTON AND CONNECTING ROD ASSEMBLIES This invention is concerned with methods of manufacturing a piston and connecting rod assembly and with such assemblies.
In engines which involve reciprocating motion of a piston in a cylinder transmitting motive force to a crank shaft, the piston is normally connected to the crank shaft by means of a connecting rod. Such a connecting rod has a "small end", which is pivotally connected to the piston, and a"bid end", which is pivotally connected to the crank shaft. The pivotal connections are necessary to accommodate the motion of the big end of the rod around the crank shaft as the latter rotates. This invention is concerned with an assembly of such a piston and connecting rod.
In most cases, the pivotal connection between a piston and a connecting rod is provided by means of a gudgeon pin (also known as a wrist pin). The pin is generally cylindrical and has an axis which extends transversely of the piston. The pin is mounted in one or more depending bosses of the piston and passes through a cylindrical hole in the small end of the connecting rod. This type of connection, however, requires substantial bosses, increasing the weight of the piston, and a relatively complex assembly operation to insert the pin in its position and retain it in said position (usually by means of spring clips). Furthermore, the machining of the bores for the pin is relatively complex.
It is an object of the present invention to provide a method of manufacturing a piston and connecting rod assembly which is simpler than the method described above and allows a reduction in weight.
The invention provides a method of manufacturing a piston and connecting rod assembly comprising mounting a small end portion of a connecting rod in a casting die and casting metal in said die to form a piston, a portion of said piston being cast around the small end portion so that the piston forms a joint with said small end portion having at least one axis about which said piston and said small end portion can pivot relative to one another.
In a method according to the invention, the gudgeon pin is eliminated, thereby reducing the complexity of the assembly operation and, it is found that the replacement of the conventional bosses and pin, by a piston portion which surrounds the small end portion of the connecting rod, enables an overall weight reduction to be achieved.
Preferably, said small end portion is coated with a separating material before being mounted in the casting die, said separating material being effective to prevent the cast metal forming the piston from adhering to said small end portion. The separating material also prevents thermal contraction of the piston as it cools from causing the piston to clamp itself on to the small end portion, which would make the joint immovable. Said separating material may comprise a lubricant which is effective to reduce friction when movement occurs about said axis. A suitable separating material is graphite which can withstand the casting temperatures normally used to cast suitable metals such as aluminium alloys and steel. The graphite can be sprayed onto the external surface of the small end portion either before or after it is mounted in the die.
After the piston has been cast, it may be subjected to stress relieving treatments or heat treated.
In a method according to the invention, the entire connecting rod may be mounted so that the small end portion thereof is in the casting die. However, in order to enable the piston to be more easily machined than would be the case if a whole connecting rod were present, said small end portion of the connecting rod may be a separate piece which is joined to the remainder of the connecting rod after the casting of said piston. In other words, the small end portion has the piston cast around it, the piston is machined and subjected to any other necessary processes, and then the small end portion is connected to the remainder of the connecting rod. For example, the small end portion may comprise a threaded portion which can make a threaded connection with the remainder of the connecting rod. Alternatively, the small end portion may be welded to the remainder of the connecting rod or any other suitable fixing method may be used.
In some cases, said small end portion may comprise a substantially ball-shaped portion around which said piston forms a cage. This enables the piston to turn relative to the connecting rod, provided that the piston is substantially circular in transverse cross-section, so that, for example, wear may be evened out.
The invention also provides a piston and connecting rod assembly wherein the piston comprises a portion which is cast around a small end portion of the connecting rod so that the piston forms a joint with said small end portion having at least one axis about which said piston and said small end portion can pivot relative to one another.
In an assembly according to the invention, the small end portion of the connecting rod may be mechanically joined to the remainder of the connecting rod.
In an assembly according to the invention, a separating coating on said small end portion may separate the piston from the small end portion.
In an assembly according to the invention, the small end portion may be in the form of a ball around which the piston forms a cage.
There now follows a detailed description, to be read with reference to the accompanying drawings, an illustrative method of manufacturing a piston and connecting rod assembly, and of an illustrative assembly made according to the illustrative method.
In the drawings: Figure 1 is a diagrammatic view of the illustrative piston and connecting rod assembly, showing some parts in section; and Figure 2 is a diagrammatic view of a stage in the illustrative method.
The illustrative piston and connecting rod assembly 10 comprises a piston 12 formed from aluminium alloy as a casting, and a connecting rod 14 which has a big end of conventional construction and a small end provided by a separate piece 16.
The big end of the connecting rod 14 comprises a bearing portion 18 which defines a semi-cylindrical bearing surface 20 which co-operates with a semi-cylindrical bearing surface 22 formed on a cap 24. The surfaces 20 and 22 co-operate in forming a cylindrical bearing surface for a crank-shaft (not shown).
The piece 16 which forms the small end of the connecting rod 14 comprises a cylindrical projection 16a which is externally screw-threaded and is received in a threaded bore 14a of the connecting rod 14. The bore 14a extends longitudinally of the rod 14 in a central portion thereof which connects the big end and the small end of the rod. The piece 16 also comprises a ball 16b which merges with the cylindrical portion 16a so that an outer surface 26 of the ball defines more than half of a sphere. The surface 26 is covered by a lubricant coating 27 which is formed from graphite.
The piston 12 comprises a crown portion 12a and a depending skirt portion 12b of conventional form. The piston 12 also comprises a central cylindrical depending portion 12c which is surrounded by the skirt portion 12b.
The portion 12c defines a recess 28 in which the ball 16b and its coating 27 are received. The recess 28 receives more than half the ball 16b so that the ball is captive in the recess 28 but is free to rotate or pivot about a transverse axis relative to the piston 12. In other words, the piston 12 forms a joint with the piece 16 in which the piece 16 can turn or pivot, ie the recess 28 forms a cage around the ball 16b.
Figure 2 illustrates the illustrative method of manufacturing the assembly 10. The method comprises mounting the piece 16 which forms the small end of the connecting rod 14 in a casting die 30. The die 30 comprises a base 32 which has a hole 34 therein which is the same shape as the portion of the piece 16 which projects beyond the cylindrical portion 12c in the downwards direction. In other words, the hole 34 has the shape of a threaded cylindrical recess, in which the portion 16a of the piece 16 is received, and of the outer surface of the coating 27 around the portion 16a. Before the piece 16 is mounted in the hole 34, the graphite coating 27 is applied to the ball 16b. The base 32 also supports a hollow cylindrical core 34 which defines the space in the piston 12 between the portions 12b and 12c thereof.
The die 30 also comprises a top 36 and two side portions 38. The base 32, the top 36 and the side portions 38 cooperate in forming a cavity in the shape of the piston 12. One of the side portions 38 defines a runner system 40 by which molten aluminium alloy can be introduced into the cavity and the top 36 defines a riser 42 up which aluminium alloy can flow out of the cavity.
After the die cavity has been assembled with the piece 16 mounted therein, the illustrative method comprises casting the aluminium alloy in the die 30 to form the piston 12. The casting is a gravity casting process in which molten aluminium is poured into the runner system 40 so that it enters the die cavity near the bottom thereof.
The molten metal flows upwardly in the die cavity and enters the riser 42. During the casting process, the coating 27 of graphite on the ball 16b prevents the metal from sticking to the ball. The coating 27 also serves to allow for thermal contraction of the piston 12 during cooling thereof.
When the metal in the die cavity has solidified, the die 30 is opened by withdrawing the side portions 38 in diametrically-opposed horizontal directions. Then the top 36 is moved upwardly away from the piston 12 which is then rotated about a longitudinally axis thereof to remove the piece 16 from the recess 34.
Once the piston 12 with the piece 16 captive therein has been removed from the die 30, the portion 16a of the piece 16 is screwed into the threaded bore 14a to complete the assembly 10.
The assembly 10 allows the connecting rod 14 and the piston 12 to pivot relative to one another to accommodate the turning of the crankshaft which is received in the surfaces 20 and 22 of the big end of the connecting rod. Furthermore, when the piston 12 has a circular transverse cross-section, the piston 12 can rotate relative to the connecting rod 14.
If desired, lubrication channels may be formed in the piston 12 to allow lubricating fluid to reach the surface 26 during service. Such channels can be formed by boring or can be cast into the piston 12.

Claims (10)

  1. CLAIMS 1 A method of manufacturing a piston and connecting rod assembly comprising mounting a small end portion of a connecting rod in a casting die and casting metal in said die to form a piston, a portion of said piston being cast around the small end portion so that the piston forms a joint with said small end portion having at least one axis about which said piston and said small end portion can pivot relative to one another.
  2. 2 A method according to claim 1, wherein said small end portion is coated with a separating material before being mounted in the casting die, said separating material being effective to prevent the cast metal forming the piston from adhering to said small end portion.
  3. 3 A method according to claim 2, wherein said separating material comprises a lubricant which is effective to reduce friction when movement occurs about said axis.
  4. 4 A method according to any one of claims 1 to 3, wherein said small end portion of the connecting rod is joined to the remainder of the connecting rod after the casting of said piston.
  5. 5 A method according to any one of claims 1 to 4, wherein said small end portion comprises a substantially ball-shaped portion around which said piston forms a cage.
  6. 6 A piston and connecting rod assembly wherein the piston comprises a portion which is cast around a small end portion of the connecting rod so that the piston forms a joint with said small end portion having at least one axis about which said piston and said small end portion can pivot relative to one another.
  7. 7 An assembly according to claim 6, wherein the small end portion of the connecting rod is mechanically joined to the remainder of the connecting rod.
  8. 8 An assembly according to either one of claims 6 or 7, wherein a separating coating on said small end portion separates the piston from the small end portion.
  9. 9 An assembly according to any one of claims 6 to 8, wherein the small end portion is in the form of a ball around which the piston forms a cage.
  10. 10 A piston and connecting rod assembly substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.
GB9826051A 1998-11-28 1998-11-28 Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod Withdrawn GB2344149A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9826051A GB2344149A (en) 1998-11-28 1998-11-28 Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod
PCT/GB1999/003896 WO2000032336A1 (en) 1998-11-28 1999-11-24 Manufacture of piston and connecting rod assemblies

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9826051A GB2344149A (en) 1998-11-28 1998-11-28 Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod

Publications (2)

Publication Number Publication Date
GB9826051D0 GB9826051D0 (en) 1999-01-20
GB2344149A true GB2344149A (en) 2000-05-31

Family

ID=10843194

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9826051A Withdrawn GB2344149A (en) 1998-11-28 1998-11-28 Manufacturing of a piston and connecting rod assembly by casting the piston around a small end portion of a connecting rod

Country Status (2)

Country Link
GB (1) GB2344149A (en)
WO (1) WO2000032336A1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB382747A (en) * 1931-10-24 1932-11-03 Ernest Talbot A method of securing cast metal to another metal
US4531269A (en) * 1981-07-06 1985-07-30 Deere & Company Method of assembling an improved heat insulated piston
EP0811760A1 (en) * 1996-06-04 1997-12-10 Toyota Jidosha Kabushiki Kaisha Method of producing a piston through casting

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763535A (en) * 1971-09-23 1973-10-09 Nl Industries Inc Method of making a ball joint linkage
US4179313A (en) * 1976-08-18 1979-12-18 N L Industries, Inc. Method of making an article having a cast-in place bearing
FR2463316A1 (en) * 1979-08-09 1981-02-20 Auboiroux Jean Inexpensive monolithic assemblies contg. parts free to rotate - where one part is used as insert in casting or moulding to make valves, ball joints, and many other mechanical assemblies
JPS5841665A (en) * 1981-09-03 1983-03-10 Toni:Kk Production of piston

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB382747A (en) * 1931-10-24 1932-11-03 Ernest Talbot A method of securing cast metal to another metal
US4531269A (en) * 1981-07-06 1985-07-30 Deere & Company Method of assembling an improved heat insulated piston
EP0811760A1 (en) * 1996-06-04 1997-12-10 Toyota Jidosha Kabushiki Kaisha Method of producing a piston through casting

Also Published As

Publication number Publication date
GB9826051D0 (en) 1999-01-20
WO2000032336A1 (en) 2000-06-08

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)