Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
1998-03-03
2003-05-13
Cuda, Irene (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S413000, C029S416000
Reexamination Certificate
active
06560869
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods of producing bearing surfaces in the opening or “eye” of a connecting rod such as used in automobile engines.
Conventional connecting rods, in particular those for internal combustion engines, are designed as so called “cut” connecting rods or “cracked” connecting rods. In this case, it is the large connecting rod eye which surrounds the crankshaft that is cut or cracked. The small connecting-rod eye generally does not need to be opened since it is connected to the piston by a straight pin which can be passed through the eye.
Connecting rod eyes are customarily fitted with one of several different bearing shells i.e., sliding bearings, depending on the load to be applied to the bearing. Backing shell materials used in particular as bearing shells are generally made of C 10 steel according to DIN Standard 17210 or SAE Standard 1010. Depending on its constructional shape and use, a bearing shell may be cold-hardened. The actual sliding layer of the sliding bearing which is applied to the backing shell material may be, for example white metal, leaded bronze, light metal, a sputter layer or the like, which is selected according to the anticipated load on the bearing. The bearing shell may be designed as a ternary, binary or solid bearing shell or in other ways. In order for the bearing shell to achieve a perfect fit after assembly, it is mounted with prestress.
The bearing shell not only constitutes a material cost factor, it also entails production expenditure and constitutes a source of error. Thus, for example, the insertion of a bearing shell or a half bearing shell may be overlooked during assembly, resulting in considerable damage to the engine.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for producing a connecting rod eye which overcomes disadvantages of the prior art.
Another object of the invention is to provide a method for producing a connecting rod bearing with reduced assembly costs.
According to the invention, a bearing shell is no longer required in a connecting rod eye, and particularly a large connecting rod eye, and possibly even both connecting rod eyes. Instead, a bearing layer is applied directly to the surface of a connecting rod eye by thermal spraying. Plasma spraying is used preferably as thermal spraying and the connecting rods are preferably parts of an internal combustion engine.
As the bearing layer a metal, and preferably a metal alloy, is sprayed on. Moreover, a mixture of different metals, preferably metal alloys, is used. In one embodiment the mixture may be, for example, a mixture of aluminum and tin, in which case the mixture is obtained particularly advantageously by mixing the individual components in powder form. The classification of the metal powder depends, inter alia, on the individual spraying parameters and can easily be determined by the person skilled in the art in a series of tests. As bearing materials, bronzes are advantageously used, in particular aluminum bronze or aluminum/tin or even copper bronze, as well as metal/soft material layers and/or metal/solid lubricant layers. Soft metals, such as lead, are used, for example, as soft materials, which are dispersed in a harder metal such as, for example, alloyed aluminum such as aluminum/copper/magnesium/chromium. However, other materials such as, for example, fluoropolymers, e.g. polytetrafluoroethylene, can also be used as soft materials. Examples of suitable solid lubricants are compounds such as molybdenum disulfide, boron nitrite and graphite.
The bearing material is sprayed on particularly advantageously to produce an oversize layer which is subsequently reworked mechanically. Honing is used, for example, for reworking. In particular, fine spindling is suitable. In the case of honing, preferably about 20 &mgr;m to 300 &mgr;m, and in particular about 50 &mgr;m to 200 &mgr;m, of the bearing material is removed. In the case of fine spindling, the oversize is advantageously 50 &mgr;m to 1000 &mgr;m, and in particular 100 &mgr;m to 500 &mgr;m.
The finished bearing layer, after removal of the oversize, is preferably about 150 &mgr;m to 800 &mgr;m thick, and in particular about 200 &mgr;m to 500 &mgr;m thick. Such a layer is far thinner than conventional bearing shells, which have a thickness of about 2.5 mm. This means that either more material around the edge of the connecting rod remains, thereby permitting a higher loading, or that connecting rods of lower weight can be produced.
According to the invention, the connecting rod eye which is coated with the bearing material by thermal spraying is advantageously separated into two parts only after the bearing material has been applied. This procedure is used particularly when the connecting rod eye is to be broken open. In this process, the inner surface of the connecting rod eye is scored with a notch at each of the desired breaking points. The notches are preferably made by a laser, in which case a beam from a solid state laser, for example, is introduced at about 45° into the connecting rod eye. The laser power used is in particular, about 5 to 10 kW. The notch preferably has a width of about 0.3 mm to about 0.8 mm and a depth of about 0.2 mm to about 0.7 mm. The breaking point is usually located approximately centrally in the connecting rod eye. Alternatively, the notch can also be made by a broaching tool, for example by impact.
The procedure followed when notching and breaking the connecting rod eye is preferably such that the connecting rod eye is first notched, then the bearing material is applied by thermal spraying, and subsequently the breaking is carried out. By this procedure, the gap which is otherwise present at the breaking point or between the individual bearing shells is reduced or eliminated. Under a high engine load, such a gap causes the oil film to tear away. By notching prior to coating of the bearing material, improved lubricating properties are achieved. Under some circumstances, breaking can also take place prior to the coating of the bearing material, which is then broken again, preferably without notching.
If the connecting rod eye is opened by being cut open, this preferably takes place before the bearing material is applied by thermal spraying. In this procedure, the connecting rod eye is cut open, and the separation surfaces of the remaining connecting rod and the connecting rod bearing cover are smoothed individually by broaching. The parts are subsequently fitted together again, provided with bores and threads and screwed together. In this case as well a notch is advantageously made at the separation point in the connecting rod eye which has been screwed together again, preferably prior to coating with the bearing material. Subsequently, the connecting rod eye is broken open again to separate the bearing layer. If the breaking takes place too unevenly in this case, the bearing layer itself has to be notched.
The honing or spindling treatment of the bearing layer to remove excess material as described above takes place particularly advantageously only after the connecting rod eye has been opened. As a result, any burr which may occur at the breaking edge when the bearing layer is broken is removed at the same time as the excess material is removed.
An oil duct can also be provided in the eye of a connecting rod produced according to the invention. The oil duct is advantageously bored into the connecting rod eye only after the bearing layer has been applied and, in particular, after the bearing layer has been reworked. In this case as well, the oil duct can be bored through the connecting rod itself so as to extend to the opposite connecting rod eye.
According to the invention, the large flat side surfaces of the connecting rod are advantageously reworked only after the bearing layer has been applied. This reworking preferably takes place by grinding the flat surfaces.
In the method according to the invention, the bearing surface of the connecting rod eye is preferably roughened prior to a
Schlegel Udo
Vogelsang Reinhard
Baker & Botts LLP
Cuda Irene
Volkswagen AG
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