Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Reexamination Certificate
2000-01-28
2002-04-09
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
C427S455000, C427S456000, C427S327000, C427S328000, C451S038000, C451S057000
Reexamination Certificate
active
06367151
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 layer which overcomes disadvantages of the prior art.
Another object of the present invention is to provide a connecting rod bearing having a high strength bearing layer.
These and other objects of the invention are attained by roughening the bearing surface of a connecting rod eye by sandblasting it with successively different particle size distributions before depositing a bearing layer by thermally spraying a bearing material on the 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 adhesive pull strength of the bearing layer, the connecting rod eye to be coated can be roughened preferably by abrasive sandblasting to be carried with sands of successively different particle-size distributions. To increase the quantity of residual oil on the bring layer, the layer can have a groove and/or is microporous.
The various particle-size distribution curves that are advantageously used according to the invention are also known as mesh size classes, where according to the invention the classes from 16 mesh to 230 mesh i.e., 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 100, 120, 140, 170, 200 and 230 in particular are used. The mesh count specifies the number of holes per square inch, i.e., per 6.45 cm
2
in the screen used. For example, the individual particle-size distribution curves, including tolerances and sieve wire sizes, can be obtained from the Handbook of Chemistry and Physics, 64th Edition, 1983/1984, CRC Press Inc., Florida, p. F-114.
It has been determined by thermally coating a connecting rod eye that the usable bearing layers, which are made of aluminum bronze for example, have a high residual layer stress which in particular is increased by the fact that the material is deposited with a low porosity. Consequently, it is clear that measures to increase the bonding strength of the bearing layer are necessary. This is advantageously achieved in accordance with the invention in that the connecting rod eye is sandblasted with successively different grain sizes including at least one fine and at least one coarse grain size distribution.
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 d
Schlegel Udo
Vogelsang Reinhard
Baker & Botts LLP
Compton Eric
Hughes S. Thomas
Volkswagen AG
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