Bearings – Rotary bearing – Plain bearing
Patent
1988-12-27
1989-12-05
Hannon, Thomas R.
Bearings
Rotary bearing
Plain bearing
29413, 74579R, 384503, F16C 3500, F16C 3364
Patent
active
048849006
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to fracture splitting of light metal components.
Fracture splitting is a known technique used, for example, in the separation of the bearing cap from the rod in an internal combustion engine connecting rod. Connecting rods are normally made in one piece, by casting or forging, and the bearing cap is subsequently separated from the rod to enable the rod to be fitted around a journal of a crankshaft. In order to ensure that the cap and the rod are properly matched, steps are taken to ensure that each cap is always paired with the rod from which it was separated.
Fracture splitting is particularly appropriate for producing this separation. The fractured edges provide, on reassembly, a unique, perfectly keyed and positively located joint thereby eliminating the need for any machining operations.
Fracture splitting has however not been possible with light metal (ie aluminium, magnesium and alloys containing either one of them) components because the inherent ductility of the material results in the fracture edges being distorted so that they do not reassemble as desired.
According to the present invention, there is provided a light metal component formed in a single piece and having an aperture entirely surrounded by the metal of the component, wherein the component can be split to separate a cap portion from the rest of the component and thereby allow a separate component to be introduced into the aperture, whereupon the cap portion can be reunited with the rest of the component to close the aperture around the separate component, characterised in that a brittle material is implanted in the metal surrounding the aperture to form a fracture zone at which the the component can be split substantially without any ductile deformation.
The cap may conveniently be reunited with the rest of the component by bolting the two together.
The brittle material may be in the form of an insert of a brittle metal. Alternatively the component may be implanted with embrittling constituents at the fracture zone.
The brittle metal insert may be a sintered steel insert. Either the component itself or the insert, or both, may be notched to provide a stress-raising crack initiation plane to provide a starting point for the fracture splitting.
Alternatively the brittle metal may be introduced as an armature of wire positioned where the brittleness is needed, with the light metal of the component cast around the wire so that the wire is included in the desired part of the component.
When the brittle material is introduced by implanting embrittling constituents in an aluminium alloy component, the embrittling constituents may, for example, be FeAl.sub.3 or FeMnAl.sub.6 which will be concentrated at the fracture zone on a macro scale.
A typical application for the invention is in the big ends of light metal engine connecting rods which are used in some engines in preference to steel because of their lighter weight. Another application is in main bearing carriers, again for internal combustion engines.
An additional advantage of the invention in these applications is a greater resistance to expansion. There is a problem when a light metal con rod supports a steel-backed bearing because of the differential rates of expansion. This problem can be ameliorated by forming the con rod with an incorporated brittle material. Furthermore, there are other benefits in terms of increased stiffness and strength.
The invention will now be further described, by way of example, with reference to the accompanying drawing, in which FIGS. 1, 2 and 3 each show a connecting rod for an internal combustion engine adapted to be split by a fracture splitting technique.
The figures show a connecting rod 10 with a big end 12 and a small end 14. This rod is made in one piece from an aluminium alloy by a squeeze casting technique. In order to be able to assemble the big end around a crankshaft journal, with an interposed bearing, it is necessary to split a "bearing cap" 16 from the rod. This splitting is to take place along the line 18.
T
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Biggs David A.
Pirault Jean P.
Rowbotham Mervyn
Ford Motor Company
Hannon Thomas R.
Malleck Joseph W.
May Roger L.
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