GB2358057A

GB2358057A - Connecting rod assembly

Info

Publication number: GB2358057A
Application number: GB0000170A
Authority: GB
Inventors: Charles Carey
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-01-06
Filing date: 2000-01-06
Publication date: 2001-07-11
Also published as: WO2001050029A1; AU2384201A; GB0000170D0

Abstract

The connecting rod 1 comprises a little end bearing 2 and a bearing surface 3 forming part of the big end opening which is completed by a cap 4, eg of sheet steel, having a bearing surface 5. During assembly, the cap 4 is drawn over the crankpin 6 and is joined to the connecting rod 1 at faces 7 eg by bolts, screws or welding. Thus the form of the big end opening is determined during assembly by the form of the crankpin either by direct contact or via spacing means. In a modification, a single bearing element 8 is attached to the connecting rod 1 and then closed around the crankpin 6 with plastic or elastic deformation. The flanges 10 of the bearing element 8 are then joined. This arrangement (a) eliminates the need for a cap and a bearing shell as separate components, (b) avoids expensive machining or fracture splitting of the connecting rod and (c) lightens the connecting rod, especially in the region of the big end opening.

Description

2358057 A connecting rod assembly.

This invention relates to a connecting rod, in particular a connecting rod for internalcombustion piston engines.

A known connecting rod comprises a body with a stem which connects an opening at one end, the small connecting rod eye or little end, to an opening at the other end, the big end, and this stem has ribs, either joined with a web or otherwise, which connect the two openings. The big end opening contains bearing shells which are held in the opening by means of a radial pressure due to an interference between the outer surface of the bearing shell and the inner surface of the opening; the inner surface of the bearing shells provides the profile of the big end bore in which the crankshaft rotates during engine operation. The big end opening is also provided With a detachable cap to permit assembly of the connecting rod to the crankshaft. The cap is attached to the main body by means of bolts or screws. The form of the big end opening is determined by prior machining of the connecting rod big end bore together with suitable selection of the bearing shells that are fitted inside this big end opening. The bearing shell may have a non uniform thickness which determines the inner surface profile and the resulting radial clearance between the crankshaft but this profile is set with respect to the form of the inner surface of the machined big end bore in the connecting rod.

This invention seeks to lighten the connecting rod particularly in the region of the big end opening and also reduce the cost of the connecting rod and big end bearing assembly.

According to the present invention there is provided a connecting rod which has the inner profile of the big end opening determined at one or more points by the form of the crankshaft which passes within the big end opening.

With the arrangement above, on assembly of the connecting rod to the crankshaft the closing of the big end opening by the fixing of a cap or otherwise is dimensionally controlled by the form and dimension of the crankshaft pin passing within the big end opening. By utilising the crankshaft as a means to determine the profile of the big end opening significant machining of the connecting rod may be avoided including some or all of the expensive and precise fine boring of the big end opening. The connecting rod may be made of two pieces, a cap and main body joined together with screws or bolts or alternatively riveted or welded for a non reusable assembly after dismantling. The main body may be constructed of a substantially metallic material and preferably may be integral with the bearing element. The cap may also be integral with the bearing element eliminating the need for two components, namely cap and bearing shell. In consequence the number of separate components, namely two bearing shells together with two connecting rod components, namely main body and cap, is reduced. With such a configuration the bearing element may still be manufactured by current processes such as casting, roll bonding, sintering or sputtering a bearing surface material onto a sheet steel backing strip. The flexibilty of such a bearing element would require the surface of the crankshaft pin to determine the form of the resulting big end opening during assembly and may result in contact between the bearing surface and the crankpin due to the non circularity of the big end bore. However the elastohydrodynarnic forces during engine operation arising from the interaction between the big end bore, oil film, and crankshaft, may deform the big end bore resulting in an inner surface profile that gives acceptable engine operation. In addition any severe regions of non circularity in the big end bore may be alleviated by wear of the bearing surface during an initial running-in period of the engine.

With this arrangement expensive machining of the connecting rod is avoided including the big end bore and the joint faces between the main body and cap; the less expensive method of fracture splitting the cap from the main body is also avoided with significant savings in cost.

Embodiments of the invention are illustrated diagrammatically in the drawing in which;- Figs 1,2 shows a side view of a connecting rod, crankpin and cap.

Figs 3,4,5 show an alternative connecting rod assembly.

2.

Referring to the drawing, Figure 1 shows a connecting rod 1 comprising a little end 2 and a bearing surface 3 to form part of the big end opening. The cap 4 has also a bearing surface 5 which comprises the other part of the big end opening. A substantially cylindrical crankpin 6 passes between the connecting rod 1 and cap 4. On assembly of the components the connecting rod 1, with or without the piston assembly attached, is drawn over the crankpin 6; the cap 4 is similarly drawn over the crankpin 6 and joined to the connecting rod at the faces 7 shown in Figure 2 by means of a bolt, screws, welding or otherwise. The form of the big end opening comprising the bearing surfaces 3 and 5 is determined by the form of the crankshaft at points a and b shown in Figure 2, either by direct contact at these points or by means of a controlled spacer or spacing mechanism.

Another embodiment of the invention is shown in Figure 3 where a single bearing element 8 with a big end opening surface 9 is attached to the connecting rod 1 by means of welding or otherwise. The complete assembly is brought over the crankpin 6 in Figure 4 and then closed around the pin in Figure 5 by either elastically andlor plastically deforming the protruding arms of the bearing element 8 around the surface of the crankpin. In this embodiment the flanges 10 are brought together to form a joint face 11 which might be closed by means of a bolt, welding or otherwise. Whereas the internal perimeter of the big end bore bearing surface is determined by the length of the bearing element 8 and position of the flanges 10, the form of the crankshaft has substantially determined the shape of the resulting big end opening. Before closing the bearing element 8 around the crankpin 6 the points c and d on the crankshaft are determining positions of the bearing surface 9 whereas during closure points e,f, and g are points which may control the big end bore bearing surface. There may or may not be contact at these points between the bearing surface 9 and crankpin 6 prior to and during engine operation.

3.

Claims

1. A connecting rod which has the inner profile of the big end opening determined at one or more points by the form of the crankshaft which passes within the big end opening.

2. A connecting rod according to claim 1, where the bearings with sheet steel backing strip form an integral part of the connecting rod.

3. A connecting rod substantially as herein described with references to and as shown in Figures 1 to 5 of the drawings.