WO2001094053A1

WO2001094053A1 - A connecting rod and a method of making a connecting rod

Info

Publication number: WO2001094053A1
Application number: PCT/GB2001/002479
Authority: WO
Inventors: Simon James Stedman
Original assignee: United Engineering Forgings Limited
Priority date: 2000-06-05
Filing date: 2001-06-05
Publication date: 2001-12-13
Also published as: GB0013673D0; AU2001262513A1

Abstract

A connecting rod (10) for an internal combustion engine has big and small ends (12, 14) defining bores, to the inner surface of one or both of which bearing material (18, 20) is applied by centrifugal casting or stirr friction welding.

Description

A CONNECTINGROD AND AMETHOD OFMAKINGA CONNECTING

ROD

The invention relates to a connecting rod for an automotive internal combustion engine and a method of making a connecting rod.

A known connecting rod for an automotive internal combustion engine is forged in a suitable steel material. The connecting rod has a big end and a small end with a bore machined in each. The bores must be ground and finished to fine tolerances both in terms of the diameter of the bores, and in terms of the distance apart of their centres. Bearing shells, which have also been fabricated to precision tolerances are then inserted into the bores.

According to one aspect of the invention therb is provided a connecting rod for an internal combustion engine, one or both of the big and small ends of the connecting rod defining a bore to the inner surface of which a bearing material has been applied by casting.

According to another aspect of the invention there is provided a method of applying a bearing material to the inner surface of the bore in the big end or small end of a connecting rod, the method comprising casting the bearing material on to the connecting rod.

According to a further aspect of the invention there is provided a connecting rod for an internal combustion engine, one or both of the big end and the small end of the connecting rod defining a bore to the inner surface of which a bearing material has been applied by stirr friction welding.

According to another aspect of the invention there is provided a method of applying a bearing material to the inner surface of a bore in the big end or small end of a connecting rod, the method comprising stirr friction welding the bearing material on to the connecting rod.

These techniques allow a relatively thick layer of bearing material to be deposited quickly and at low porosity. All that is then required is for the bearing material itself to be ground and finished, if required, to the necessary tolerances. This avoids the tolerances between the bearing shells and the precision finished bores and removes the step of fitting the bearing shells, thus reducing cost and reducing the time taken to complete manufacture. In some instances, finishing may not be required at all. Also, unlike the known method, the bore in the connecting rod that is ground and finished provides the final bearing surface and so there is greater precision in the dimensions of the bores and the distance apart of their centres. The fact that a relatively thick layer of material is deposited means that gross discrepancies in the size and positioning of the bores before application of the bearing material can be overcome.

According to another aspect of the invention there is provided a connecting rod for an internal combustion engine, one or both of the big and small end of the connecting rod defining a bore to the inner surface of which a bearing material has been applied, the bearing material having less than 2% porosity and being more than 0.1 mm thick in the radial direction of the bore.

Where the bearing material is cast, any suitable type of casting method may be used. Thus the bearing material may be applied by squeeze casting thixotropic casting, or by die casting under high pressure or with gravity feed. With the use of a suitable polymer material, the bearing material could be injection moulded. Preferably however the bearing material is cast by centrifugal casting. This allows, rapid and accurate casting with relatively low tooling cost. It also avoids the porosity which often occurs in the other casting methods due to solidification shrinkage. Centrifugal casting allows the application of a very uniform layer of material of very uniform thickness. A further advantage of centrifugal casting is that all of the slag or other impurities (if present) tend to end up at the inner diameter of the casting. These impurities are therefore easily removed and may be removed in the course of finishing steps which would be carried out in any case. Thus no additional process steps may be required to result in a higher purity layer on the finished product.

Any suitable bearing material may be used, such as copper based alloys, like copper lead or leaded bronze, or aluminium based alloys, like aluminium-tin, aluminium-lead and aluminium-silicon. In one preferred embodiment the bearing material is a high silicon content aluminium alloy. The rapid cooling rates achieved by the use of centrifugal casting would allow the use of this material which is known to be difficult to cast by other methods.

Preferably, at least two materials are applied to the con rod. One of the materials may be for trapping or embedding foreign particles. The material may thus be soft or compliant and, by trapping or embedding foreign particles the material can prevent damage to the main supporting bearing material. The materials may be laid down in any suitable way and may be applied as separate layers or together. In one preferred embodiment, the materials have different elastic moduli. In particular, preferably, there is a top layer of bearing material and, underneath that, a layer of material of higher elastic modulus. Such a compliant layer can compensate for the very small out of roundness that can occur with the crankshaft pin or any out of roundness of the applied connecting rod bearing before or after machining. In an alternative embodiment, one material forms particles in a matrix of the other material.

Embodiments of the invention will now be described by way of example

First Embodiment

The first embodiment employs known apparatus for centrifugal casting. A forged con rod is mounted in the centrifugal casting apparatus for rotation about the centre of the bore in the big end. A counterweight is provided for the weight of the small end. A feed tube is located within the bore in the big end and a bearing material consisting of Al 83%, Cu 1%, Si 4%, Sn 12% is centrifugally cast on to the internal surface of the bore to form a layer 1.5 mm thick. The porosity of the layer is less than 2%. A bearing shell is subsequently fitted to the small end in the usual way and the big end bore is ground and finished to provide the required tolerances in diameter of the big end bore and centre to centre tolerances between the big and small end bores.

Second Embodiment This embodiment is similar to the first embodiment and only the differences between the embodiments will be described. In this embodiment the casting material is Cu 74%, Pb 24%, Sn 2% which is laid down as a 1.5 mm thick layer into the big end bore. The connecting rod is then reversed so that the small end bore is aligned in the casting apparatus. The counterweight is changed appropriately and the small end bore has the same bearing material applied in a thickness of 105 microns. There is less than 2% porosity in the layers which are thus over 98% dense.

In other embodiments the layers may be of different thicknesses and the bearing material in the small end bore may be up to several millimetres in thickness.

Third Embodiment

The third embodiment is similar to the second embodiment and only the differences between the embodiments will be described. In the third embodiment two materials are deposited simultaneously. One material is the white metal bearing material Cu 3%, Sb 7.5%, Sn 89.5%, while the other material is Al 79%, Cu 1.0%, Sn 20%. The total layer thickness is 250 microns. The resulting deposit has a "plum pudding" structure. After finish machining, the bearing material surface consists of islands of soft white metal in the harder matrix. Any hard foreign particles which find their way into the big end bore between the con rod and ^"the crankshaft in use will tend to become trapped and embedded in the softer material reducing potential damage to the actual bearing surface. The soft islands also improve conformability and compatibility.

In other embodiments a different total thickness may be used of up to several millimetres.

In each of the embodiments the con rod may be manufactured from a suitable fracture splittable material, such as the steel C70 S6 BY, and the con rod after centrifugally casting can be fracture split. The pre-notch for fracture splitting may be broached or laser cut, for example, and preferably penetrates through the bearing material so that it is only the material of the con rod itself which is actually fracture split. The pre-notch can, however, be made prior to the application of bearing material.

Fourth Embodiment

In this embodiment, the bearing material is applied to the bore in the small end of the con rod by stirr friction welding. The bearing material used is Cu 74%, Pb 24%, Sn 2%. A conventional bearing shell is fitted into the bore in the big end of the con rod. The thickness of the bearing material layer in the bore in the small end of the con rod is 1.5 mm and the density of the material is more than 8600 kg/m.3.

Fifth Embodiment

Figure 1 illustrates the fifth embodiment. A con rod 10 is shown having a big end 12 and a small end 14. The big end of the forged steel con rod is clamped between a pair of clamp rings 16. A counterweight (not shown) is used to take account of the weight of the small end. A first layer 18 is then applied by centrifugal casting. The layer 18 consists of a white metal based alloy of 0.35% lead, 4.0% copper, 8.0% antimony and the balance tin. A further layer is subsequently applied by centrifugal casting on top of the white metal layer. The second layer 20 is 85% aluminium, 1% copper, 4% silicon and 12% tin.

The white metal based material of the first layer 18 has relatively low yield strength which could yield on tightening of the bolts if there is a slight out of roundness and compensate for the out of roundness. The top layer 20 is a harder material which has good wear resistance to provide a prolonged bearing life.

In a further embodiment, the two layers of the fifth embodiment may be deposited on top of a first layer of low cost material which is used as a filler to compensate for inconsistencies and to provide a smooth surface upon which the other layers can be deposited. As shown in Figure 1, the clamp rings clamp on to the thrust faces 22 of the big end 12 so that the bearing material laid down as the first layer 18 is allowed to escape from the big end bore and coat the thrust faces 22. This therefore provides a bearing on the thrust face.

The small end bore can have a bearing applied in the same manner as the big end bore.

Bonding between the cast material and the connected rod may be promoted by cleaning and coating the forged steel con rod with a thin layer of tin or other coatings such as silicon. The cleaning can be achieved physically or by the use of a flux.

Claims

1. A connecting rod for an internal combustion engine, one or both of the big and small ends of the connecting rod defining a bore to the inner surface of which a bearing material has been applied by casting.

2. A connecting rod as claimed in claim 1, wherein the bearing material is cast by centrifugal casting.

3. A connecting rod as claimed in claim 1 or claim 2, wherein the bearing material is a high silicon content aluminium alloy.

4. A connecting rod as claimed in claim 1, 2 or 3, wherein the bearing material has less than 2% porosity and is more than 0.1 mm thick in the radial direction of the bore.

5. A connecting rod for an internal combustion engine, one or both of the big end and the small end of the connecting rod defining a bore to the inner surface of which a bearing material has been applied by stirr friction welding.

6. A connecting rod as claimed in claim 5, wherein the bearing material has less than 2% porosity and is more than 0.1 mm thick in the radial direction of the bore.

7. A connecting rod for an internal combustion engine, one or both of the Trig and small ends of the connecting rod defining a bore to the inner surface of which a bearing material has been applied, the bearing material having less than 2% porosity and being more than 0.1 mm thick in the radial direction of the bore.

8. A connecting rod as claimed in any preceding claim wherein at least two materials are applied to the con rod.

9. A connecting rod as claimed in claim 8, wherein the two materials or at least two of the materials are applied together.

10. A connecting rod as claimed in claim 9, wherein one of the materials is soft and compliant to trap or embed foreign particles.

11. A connecting rod as claimed in claim 8, wherein two of the materials or at least two of the materials are applied as separate layers.

12. A connecting rod as claimed in claim 11, wherein the materials have different elastic moduli.

13. A connecting rod as claimed in claim 12, wherein there is a top layer of bearing material, and underneath that, a layer of material of low elastic modulus.

14. A method of applying a bearing material to the inner surface of the bore in the big end or small end of the connecting rod, the method comprising casting the bearing material on to the connecting rod.

15. A method as claimed in claim 14, wherein the bearing material is cast by centrifugal casting.

16. A method as claimed in claim 14, wherein the bearing material is a high silicon content aluminium alloy.

17. A method as claimed in claim 14, 15 or 16, wherein the bearing material is cast to have less than 2% porosity and to be more than 0.1 mm thick in the radial direction of the bore.

18. A method of applying the bearing material to the inner surface of the bore in the big end or small end of the connecting rod, the method comprising stirr friction welding the bearing material on to the connecting rod.

19. A method as claimed in claim 18, wherein the bearing material is applied to have less than 2% porosity and to be more than 0.1 mm thick in the radial direction of the bore.

20. A method as claimed in any of claims 14 to 19, wherein at least two materials are applied to the con rod.

21. A method as claimed in claim 20, wherein the two materials or at least two of the materials are applied together.

22. A method as claimed in claim 21, wherein one of the materials is soft and compliant to trap or embed foreign particles.

23. A method as claimed in claim 20, wherein the two materials or two of the materials are applied as consecutive layers.

24. A method as claimed in claim 23, wherein the materials of the layers have different elastic moduli.

25. A method as claimed in claim 24, wherein a layer of a material of lower elastic modulus is applied followed by a top layer of bearing material.