Patent Publication Number: US-RE39613-E

Title: Half bearing with grooves preventing leakage of lubricating oil

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a half bearing constituting a cylindrical plain bearing when two of the half bearings are combined together. 
     2. Description of the Related Art 
     A plain bearing is used to support a rotating shaft such as a crankshaft of an internal combustion engine, for example. The plain bearing is made by combining two generally semicylindrical half bearings into a cylindrical form. A lubricating oil is supplied between an inner circumferential surface of the plain bearing and the rotating shaft so as to form an oil film. 
     Conventional half bearings constituting the plain bearing have crush relief surfaces formed on inner circumferential surfaces of both circumferential ends thereof respectively. The crush relief surfaces are formed so as to spread substantially over an entire width of the bearing or axial dimension of the bearing with respect to a shaft supported by the bearing. When a plain bearing is assembled into a bearing housing, joints of the respective half bearings sometimes shift from each other. Furthermore, when a crush height of the bearing is excessively high, the bearing is sometimes brought into a local contact with the shaft as the result of a radially inward swelling due to deformation in the vicinity of the joint. The aforesaid crush relief surfaces prevent the shift of the joints and the local contact. In the conventional half bearings, however, a large amount of lubricating oil leaks axially from each crush relief surface. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a half bearing which can reduce an amount of lubricating oil leaking therefrom with the function of the crush relief surface being maintained. 
     To achieve the object, the present invention provides a half bearing constituting a cylindrical plain bearing for supporting a shaft for rotation when two of the half bearings are combined together, the half bearing having two circumferential ends each of which has a plurality of circumferential grooves without formation of any crush relief surface, wherein the grooves extend substantially over an overall circumferential dimension of the half bearing and include portions located at both circumferential ends of the half bearing respectively, each portion having a larger axially sectional area than the grooves formed in a portion of the half bearing mainly subjected to load during rotation of the shaft. 
     The half bearing is formed with a plurality of the circumferential grooves in the inner circumferential surfaces of both circumferential ends thereof although no crush relief surface is formed there. Protrusions defined between the grooves tend to be easily configured to the shaft to be worn due to contact with the shaft. Accordingly, when the half bearings are combined together into a plain bearing, the protrusions are conformed to the shaft to be worn at an early stage such that worn portions serve as crush relief surfaces. Thus, the function of the crush relief surface can be achieved although the half bearing is formed with no crush relief surfaces. A region serving as the crush relief surfaces is minimum in this case. As a result, an amount of lubricating oil leaking in the half bearing can be smaller than in a case where a half bearing is positively provided with crush relief surfaces. Moreover, the half bearing can prevent an axial leakage of the lubricating oil more effectively since the grooves extend circumferentially. 
     Furthermore, the grooves extend substantially over an overall circumferential dimension of the half bearing and include portions located at both circumferential ends of the half bearing respectively. Further, each of said portion has a larger axially sectional area than the grooves formed in a portion of the half bearing mainly subjected to load during rotation of the shaft. A large amount of lubricating oil can be supplied without reduction in a load capacity of the portion mainly subjected to load during rotation of the shaft. Consequently, an anti-seizure property and a sliding characteristic can be improved. 
     In a preferred form, said portions of the grooves located at both circumferential ends respectively are deeper than the grooves formed in the portion of the half bearing mainly subjected to load during rotation of the shaft. In addition to the effect of increasing an amount of lubricating oil fed to the portion mainly subjected to the load, the protrusions located at both circumferential ends tend to be easily conformed to the shaft to be worn with contact with the shaft since the protrusions have a lower strength than those located between the grooves of the portion mainly subjected to the load during rotation of the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become clear upon reviewing the following description of embodiments, made with reference to the accompanying drawings, in which: 
         FIG. 1  is a front view of the half bearing of a first embodiment in accordance with the present invention; 
         FIG. 2  is a developed view of the half bearing, showing an inner circumferential surface thereof; 
         FIG. 3A  is a partially enlarged sectional view taken along line  3 A— 3 A in  FIG. 2 ; 
         FIG. 3B  is a partially enlarged sectional view taken along line  3 B— 3 B in  FIG. 2 ; 
         FIG. 4  is a longitudinally sectional front view of a plain bearing comprising the half bearings of the embodiment; and 
         FIG. 5  is a view similar to  FIG. 2 , showing a half bearing of a second embodiment in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to  FIGS. 1  to  4 . Referring to  FIGS. 1 and 2 , a half bearing  1  of the embodiment is generally formed into a semicylindrical shape. The half bearing  1  has both circumferential ends  2 b each of which has no crush relief surface. 
     The half bearing  1  includes an inner circumferential surface  1 a formed by boring using cutting tools (not shown). The inner circumferential surface  1 a has a plurality of circumferentially continuously extending grooves  3  substantially over an overall surface. The grooves  3  include shallow grooves  3 a falling within two continuous ranges of 45 degrees in opposite directions respectively from a perpendicular on a midpoint on a straight line between both circumferential ends of the half bearing, as shown in FIG.  1 . The grooves  3  further include deep grooves  3 b falling within two separate ranges of 45 degrees located adjacent to the continuous ranges of the shallow grooves  3 a at the opposite circumferential ends respectively, as shown in FIG.  1 . The grooves  3 b are deeper than the grooves  3 a as shown in  FIGS. 1 ,  3 A and  3 B. In  FIG. 1 , bottoms of the shallow and deep grooves  3 a and  3 b are represented by dotted line. In  FIG. 2 , the shallow grooves  3 a are represented by dotted line whereas the deep grooves  3 b are represented by solid line for discrimination therebetween. Further, axially middle portions of the grooves  3  are eliminated in FIG.  2 . 
     Referring now to  FIGS. 3A and 3B , protrusions or ridges  4 a are formed between the shallow grooves  3 a. Protrusions or ridges  4 b are also formed between the deep grooves  3 b. Each groove  3 a has a depth A 1  from the protrusion  4 a to the bottom, which depth A 1  is about 0.0015 mm (about 1.5 μm). Each groove  3 b has a depth A 2  from the protrusion  4 b to the bottom, which depth A 2  is about 0.005 mm (about 5 μm). A pitch between the protrusions  4 a and a pitch between the protrusions  4 b are equal to each other and about 0.3 mm. Accordingly, each of the deep grooves  3 b located at both circumferential ends has a larger sectional area than each of the shallow grooves  3 a located near the central portion  2 a and mainly subjected to load during rotation of a shaft, as will be described later. 
     Referring to  FIG. 4A , a plain bearing made by combining two half bearings  1  described above is shown. Two half bearings  1  are combined together between upper and lower bearing housings  5 a and  5 b into a generally cylindrical shape, thereby constituting a cylindrical plain bearing  6 . A shaft  7  such as a crankshaft is fitted into the bearing  6 . A lubricating oil is supplied between an inner circumferential surface of the bearing  6  and the shaft  7  so that an oil film is formed. 
     While the shaft  7  is being rotated in the direction of arrow C in  FIG. 4 , a shaft load of the shaft  7  is received mainly by a portion D of the inner circumferential surface  1 a of the lower half bearing  1  slightly to the right of the central portion  2 a (in the same direction as the shaft  7  is rotated) due to an oil film produced by rotation of the shaft. A thickness of the oil film becomes minimum at the portion D, and the portion D depends on an operating condition. The portion D can be forecast. The portion D corresponds to the shallow grooves  3 a on the inner circumferential surface of the half bearing  1 . 
     According to the above-described embodiment, the grooves  3  formed in the inner circumferential surface  1 a of the half bearing  1  include the deep grooves  3 b which are located at both circumferential ends thereof and which are deeper than the shallow grooves  3 a located at the portion D mainly subjected to the shaft load during rotation of the shaft  7 . Accordingly, each deep groove  3 b has a larger sectional area than the each shallow groove  3 a. As a result, each of the protrusions  4 b formed between the deep grooves  3 b located at both circumferential ends  2 b has a lower strength than each of the protrusions  4 a between the shallow grooves  3 a. Accordingly, each protrusion  4 b located at both circumferential ends tends to be easily conformed to the shaft  7  to be worn with contact with the shaft  7 . 
     When the above-described half bearings  1  are combined together into the plain bearing  6 , the protrusions  4 b between the deep grooves  3 b at both circumferential ends  2 b are conformed to the shaft  7  to be worn in an early stage with contact with the shaft  7  being rotated. Each worn portion serves as a crush relief surface. Thus, the function of the crush relief surface can be achieved although the half bearing  1  is formed with no crush relief surfaces. Since a region serving as the crush relief surfaces is minimum in this case, an amount of lubricating oil leaking in the half bearing  1  can be smaller than in a case where a half bearing is positively provided with crush relief surfaces. Moreover, the half bearing  1  can prevent an axial leakage of the lubricating oil more effectively since the deep grooves  3 b extend circumferentially. 
     Furthermore, the shallow grooves  3 a are circumferentially continuous with the deep grooves  3 b. Since the lubricating oil smoothly flows along the grooves  3 , a larger amount of lubricating oil can be supplied to the portion D mainly subjected to load during rotation of the shaft  7 . Consequently, an anti-seizure property and a sliding characteristics of the plain bearing can be improved. 
     It is considered that the grooves  3  formed in the inner circumferential surface  1 a of the half bearing  1  include only the deep grooves  3 b. In this construction, an oil film tends to be easily broken in the portion D mainly subjected to the load during rotation of the shaft  7 , whereupon the bearing performance is lowered. On the other hand, it is considered that the grooves  3  include only the shallow grooves  3 a. However, since wear of the protrusions  4 a due to conformance to the shaft  7  cannot be expected, the function of the crush relief surface cannot be achieved. 
       FIG. 5  illustrates a second embodiment of the invention. Only the difference between the first and second embodiments will be described. In the second embodiment, grooves  10  are formed only in both circumferential ends  2 b of the inner circumferential surface  1 a of the half bearing  1 . The other portion of the inner circumferential surface  1 a including the portion D mainly subjected to the shaft load has no grooves. 
     The invention should not be limited by the foregoing embodiments. Various modifications and expansions are possible. For example, the depth of each groove formed in the inner circumferential face  1 a may continuously be reduced as each groove extends from each of both circumferential ends  2 b to come near the main load-receiving region D. 
     The region of the shallow grooves  3 a preferably includes the portion D mainly subjected to the shaft load and ranges between 30 and 60 degrees rightward and leftward from the perpendicular on the midpoint on the line between the circumferential ends of the half bearing  1 . The remaining both circumferential ends preferably include the deep grooves  3 b. Accordingly, the regions of the shallow and deep grooves  3 a and  3 b may or may not be in a bilateral symmetry. 
     The shallow and deep grooves  3 a and  3 b may be discontinuous. Furthermore, of the grooves, those located at both circumferential ends of the half bearing may be formed as follows in order that each of these grooves may have a larger sectional area than each groove in the portion D mainly subjected to the shaft load. That is, each of the grooves formed in both circumferential ends is formed so as to be as deep as each groove in the portion D mainly subjected to the shaft load and so that a pitch between the grooves in both circumferential ends is larger than that in the portion D. In this construction, too, the sectional area of each groove located at both circumferential ends can be rendered larger than each groove in the portion D mainly subjected to the shaft load. Additionally, the grooves  3  may be formed only in both axial ends. 
     The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.