Abstract:
A journal bearing has a lining of bearing metal applied to a steel backing. The surface of the lining is laser peen hardened to locally increase the hardness and the seizure resistance of the lining. The underlying core of the lining is unaffected and maintains good conformability of the lining. The overall lining thus possesses both good seizure resistance and conformability.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application is a division of U.S. application Ser. No. 10/264,938, filed on Oct. 3, 2002.  
         [0002]     1. Technical Field  
         [0003]     This invention relates generally to journal or engine bearings for internal combustion engines, and more particularly to the construction of linings for journal bearings.  
         [0004]     2. Related Art  
         [0005]     Sliding-type journal or engine bearings are typically used in internal combustion engine applications for journaling a shaft of the engine. Typical engine bearings have an arcuate steel backing onto which one or more layers of relatively softer bearing metal is applied.  
         [0006]     The steel backing provides structural rigidity to the bearing whereas the applied bearing layer or layers provide a low friction sliding surface that must exhibit a combination of seemingly incompatible properties of acceptable wear and fatigue resistance, and acceptable conformability and seizure-resistance. The first two properties call for a hard, strong bearing material, whereas conformability and seizure resistance call for a softer material of lesser strength. It is generally accepted that no one material can satisfy all criteria, since a material cannot be both hard and soft. Accordingly, the current practice is to select a material, or multiple layer materials, that compromise between the competing properties. However, the demand for ever-increasing performance of engine bearings continues to challenge ability to provide a suitable “compromise” bearing material at an acceptable cost.  
         [0007]     Modern bearings and those of the future require ever-increasing wear and fatigue resistance properties without sacrificing the conformability of the bearings. As the demands of these competing properties get driven further apart, a suitable compromise material(s) is becoming more difficult to attain.  
         [0008]     It is an object of the present invention to overcome or greatly minimize the foregoing limitations of prior engine bearings.  
       SUMMARY OF THE INVENTION  
       [0009]     An engine bearing for an internal combustion engine has a lining with a hardened surface layer providing the journal bearing with an extended life in use. The bearing has an arcuate backing comprised of a first material having an outer surface and an inner surface. A lining comprised of a second material different from the first material is fixed to the inner surface of the backing. According to the invention, the lining is laser peened (also known as “laser shock hardened”) to impart compressive residual stresses in a surface region to produce a hardened skin with enhanced fatigue and wear resistance while an underlying core of the lining is unaffected and possesses good conformability and seizure resistance.  
         [0010]     One advantage of the present invention is that a journal type bearing is provided having an extended life in use.  
         [0011]     Another advantage of the invention is that a greater variety of bearing metals are available that can satisfy the competing properties of fatigue resistance and conformability. 
     
    
     THE DRAWINGS  
       [0012]     These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:  
         [0013]      FIG. 1  is a perspective view of a presently preferred embodiment of a journal bearing embodying the present invention;  
         [0014]      FIG. 2  is a cross sectional view taken along the line  2 - 2  of  FIG. 1 ; and  
         [0015]      FIG. 3  is an enlarged and magnified plan view of one-half of the journal bearing of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0016]     A presently preferred embodiment of a journal bearing constructed according to the present invention is shown generally at  10  in  FIGS. 1-3 . The journal bearing  10  has a backing plate  12  and a lining  14 . The backing plate  12  provides rigidity to the journal bearing  10 .  
         [0017]     The backing plate  12  is formed of a first material, preferably steel, and has an outer arcuate convex surface  18  and an inner arcuate concave surface  20 .  
         [0018]     The lining  14  is formed from a second lining material different than that of the backing plate material. Preferably, the lining material comprises either an aluminum-based or copper-based alloy material. The lining  14  has a first side  22  and a second side  24 . The first side  22  of the lining  14  is fixed to the inner surface  20  of the backing plate  12 . The second side  24  of the lining  14  defines an inner arcuate bearing surface  16  that is spaced radially inwardly from the backing plate  12 .  
         [0019]     To improve the strength characteristics of the bearing surface  16 , the second side  24  of the lining  14  is treated by laser peening or laser shock peening, which is known per se for the treatment of materials generally, but not known in connection with engine bearings to increase fatigue resistance while preserving conformability and seizure resistance of a bearing lining material. The laser peened treatment induces residual compressive stresses which serve to locally harden outer layer region  26  of the lining  14 . The hardened layer  26  improves the fatigue resistance of the bearing surface  16  by inhibiting crack initiation and propagation within and through the bearing surface  16 . As a result, the service life of the journal bearing  10  is extended.  
         [0020]     The laser surface peening process subjects the second side  24  of the lining  14  to a laser pulse with a power density of approximately 1 gigawatt/cm 2  with an interaction time of approximately 1 microsecond.  
         [0021]     The lining  14  has a non-laser peened layer or core  28  between the hardened layer  26  and the backing  12 . Typically, upon laser peening the second side  24 , the hardened layer  26  takes on a hardness value ranging anywhere between 0-5 points on the Vickers scale greater than the hardness of the core  28 , though this range can be increased depending on the laser surface peening parameters. Though the bearing surface  16  is harder than the core layer  28  of the lining  14 , the bearing surface  16  and core  28  retain a combined desirable level of conformability, with the core  28  exhibiting greater conformability than that of the hardened layer  26 .  
         [0022]     The hardened layer  26  preferably extends to a depth of about 20 to 50 micrometers below the surface  16 . As such, the conformability of the core  28 , and thus the overall lining is largely unaffected, as the conformability has been formed to be influenced primarily within a depth of ¼-½ mm below the bearing surface  16 . Conformability of the journal bearing is particularly beneficial in applications that are prone to misalignment of the shaft relative to the journal bearing, thus causing an effect commonly referred to as “edge loading.” In addition, any imperfections in machining of the shaft, such as a crank shaft in an internal combustion engine, can reduce the useful life of the journal bearing  10  if adequate conformability is not provided in the lining  14  of the journal bearing  10 .  
         [0023]     In journal bearing applications it is common for contaminants or debris to come in contact with the journal bearing  10 . Thus, it is desirable to provide journal bearings that can operate in the presences of contaminants or debris without negatively impacting the useful life of the journal bearings. The journal bearing  10 , having a bearing surface  16  and a hardened layer  26  does not impair the embedability properties of the journal bearing  10  to retain contamination or debris within the bearing surface  16 .  
         [0024]     According to a further aspect of the invention, the laser peening may be advantageously controlled to develop a particular textured surface  30  of the hardened layer  26 . For example, as best shown in  FIG. 3 , the surface texturing  30  provides for circumferentially extending grooves, represented here as a plurality of generally parallel grooves, promoting the retention of lubrication and enhanced hydrodynamic action on the bearing surface  16  of the journal bearing  10 . The surface texturing  30  is formed during the laser surface peening process by directing the shock waves to the desired location on the second side  24  of the lining  14 . While a grooved texture is illustrated by way of example, the invention contemplates other textures, for example, grooves in other directions, such as axial grooves.  
         [0025]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.