Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-01-28
2003-02-04
Vidovich, Gregory M. (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C029S898120, C029S898130, C384S430000, C384S469000, C427S446000, C427S455000, C427S456000, C427S327000
Reexamination Certificate
active
06513238
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods for producing connecting rods having a thermally sprayed bearing layer and to connecting rods produced thereby.
Conventional connecting rods now in use, especially for internal combustion engines, are so-called cut or cracked connecting rods in which the large connecting rod eye that surrounds the crankshaft is cut or cracked to open it. As a rule, the small connecting rod eye does not need to be opened since it is connected to the piston by a straight bolt.
Depending upon the load applied to the bearing, connecting rod eyes are made with a variety of bearing shells providing the friction surface. In particular, supporting shell materials used in bearing shells are as a rule made of C 10 steel according to DIN 17210 or SAE 1010. Depending upon the particular design and application, the bearing shells may be cold hardened. The actual bearing surface layer, which may, for example, be white metal, leaded bronze, light metal, spatter coatings or the like depending upon the expected bearing load, may be applied to the supporting shell material. The bearing shells may be three-component, two-component or solid single component bearing shells. The shells are assembled to the connecting rod eye with an initial stress so that the bearing shells have a satisfactory, firm seat upon assembly.
Bearing shells not only constitute a substantial cost factor, but also complicate production and are a potential source of error. For example, the insertion of a bearing shell or bearing shell half may be overlooked in assembly, resulting in considerable engine damage.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a connecting rod with a thermally sprayed bearing, and a method of making it, which overcomes disadvantages of the prior art.
Another object of the present invention is to provide a connecting rod bearing producing excellent lubrication.
These and other objects of the invention are attained by thermally spraying bearing material onto the surface of a connecting rod eye to provide a bearing surface containing micropores or a groove. In a preferred embodiment one or more circumferential grooves are formed around the inner bearing surface.
Thus, according to the invention, a bearing shell is no longer inserted into a connecting rod eye, either the large eye, or alternatively into both connecting rod eyes. Instead, a bearing layer is applied directly to the connecting rod eye by thermal spraying such as by plasma spraying. Specifically, the connecting rods made in this way are used in an internal combustion engine to connect the crankshaft to the pistons. To increase the quantity of residual oil retained by the bearing layer, the applied bearing layer has micropores and/or one or more grooves.
Operationally reliable connecting rod bearings require a wear-resistant design and construction in order to transmit the bearing forces reliably and at permissible operating temperatures. Wear resistance is always provided when the sliding surfaces are separated from each other by a lubricating film such as an oil film that is capable of bearing a load. Such a lubricating film is maintained in friction bearings by a slightly eccentric shaft mounting. With this arrangement, the rotating shaft has a pumping effect that feeds the lubricant such as motor oil into the eccentric bearing slot, and oil pressure is built up at the convergent surfaces of the bearing slot. In other words, the lubricant is pressed into the narrowest cross section of the space between the bearing surfaces. This results in a condition called “interfacial lubrication” in which there is interfacial friction of the bearing material on the journal when the rotary motion of the shaft begins or is very slow. An increase in rotation speed causes the oil film to assist in supporting the journal even though a coherent oil film has not yet been built up. This is a condition called “mixed friction,” i.e., simultaneous interfacial and floating friction. This condition exists chiefly when an engine is being started and stopped. An additional increase in the speed of rotation causes the development of the hydrodynamically supporting lubricating film layer having a thickness equal to half of the bearing clearance resulting in a condition called “floating friction.” With floating friction the bearing clearance is usually equal to about 15 &mgr;m to 60 &mgr;m.
When the surface of a connecting rod eye such as the large eye is plasma coated with an appropriate bearing material having micropores and/or a groove according to the invention, a high oil retention volume is obtained within the connecting rod bearing. As a result, friction and hence wear of the parts moving against each other, in particular during interfacial lubrication and mixed friction, are reduced. The oil retention volume is distinctly improved by the provision of at least one groove in the connecting rod bearing surface, the groove or grooves being preferably in the form of circumferential grooves. For an additional increase in oil retention capacity, the grooves are left at least largely unfinished, i.e., with their raw surface structure as produced.
In every bearing condition, regardless of the rotation speed and oil pressure, the microporous but pressure-stable structure of the sliding bearing surface, which preferably is machined, and the unfinished groove having a very rough surface structure cause a certain portion of oil to be stored in the bearing. This makes it possible for the bearing to pass through the conditions of interfacial and mixed friction more quickly even at a low crankshaft speed and hence reach the condition of nearly wear-free hydrodynamic lubrication rapidly. In other words, engine bearing performance characteristics during starting and slow-down of the engine are substantially improved so that higher bearing loads are possible with bearings having the same dimensions.
The invention has the following advantages: The bearing shells which were formerly customary in connecting rods to provide the sliding bearing surface are eliminated since, according to the invention, the bearing layer is applied directly to the connecting rod eye surface and not to an extra element inserted in the connecting rod eye. Hence, the necessity for assembly of bearing shells in the eye is also eliminated. Elimination of the bearing shells and of machining of the sliding bearing shell surface according to the invention results in a reduction of dimensional tolerance variations. There are three tolerances in conventional connecting rod bearings, the first tolerance being that of the crankshaft dimensions, while the second tolerance is determined by the dimensions of the bearing shells providing the sliding layer in the connecting rod and the third tolerance is determined by the dimensions of the connecting rod eye into which the bearing shell is inserted. As a result of coating and finishing of the bearing layer directly on the connecting rod eye surface according to the invention, the third tolerance is eliminated. In addition, according to the invention a greater thickness of connecting rod material is provided in the bolt region surrounding the eye since the bearing layer applied according to the invention is thinner than a bearing shell. This permits higher loads to be applied to the bearing of a connecting rod having the same external dimensions. The dimension of the third tolerance, i.e., the dimension of the connecting rod eye, may be sized very roughly in the present invention, since the eye is covered by the subsequent coating which is partially removed during formation of the sliding surface by, for example, fine spindling, to provide the second tolerance dimension.
According to the invention, the bearing layer is sprayed on so that it has a certain degree of porosity, at least at the bearing surface. This porosity is obtained by providing the bearing layer with micropores that are formed, for example, by oxide inclusions which are removed during finishing of the surface of
Baker & Botts LLP
Compton Eric
Vidovich Gregory M.
Volkswagen AG
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