Patent Publication Number: US-2018031031-A1

Title: Slide bearing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the U.S. national stage of application No. PCT/JP2016/055953, filed on Feb. 26, 2016. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2015-039115, filed on Feb. 27, 2015, the disclosures of which are also incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a technique of a sliding bearing, and can be applied to a sliding bearing including half members, obtained by splitting a cylinder in half in a direction parallel with an axial direction, arranged in an upper and lower direction. 
     BACKGROUND ART 
     Conventionally known sliding bearings, for supporting a crankshaft of an engine, having a split structure in which two members obtained by splitting a cylindrical member in half are combined are plagued by a large friction due to high viscosity of oil during a cold engine operation. Thus, one known bearing has relief portions (narrow grooves) formed over the entire circumference in both ends of the bearing in an axial direction (for example, see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Translation of PCT International Application Publication No. JP-T-2003-532036 
     SUMMARY OF INVENTION 
     Technical Problem 
     Such a conventional bearing in which the narrow grooves are formed fails to achieve both a larger quantity of lead-in oil and a smaller quantity of outflow oil flowing through both ends in the axial direction. Thus, a further friction reducing effect has been unable to be expected. 
     Thus, the present invention is made in view of the problem described above, and provides a sliding bearing that can achieve a smaller total quantity of outflow oil as well as a further friction reducing effect. 
     Solution to Problem 
     The problem of the present invention is as described above. Next, a solution of the problem is described. 
     The present invention is a sliding bearing including half members, obtained by splitting a cylinder in half in a direction parallel with an axial direction, arranged in an upper and lower direction. A narrow groove extending in the circumference direction is formed on an axial direction end of one of the half members on a lower side, on a downstream side in a rotation direction. A circumference edge portion is formed on an outer side of the narrow groove in an axial direction, and is formed to be lower than a contact surface of the sliding bearing to be in contact with a shaft. 
     Projecting portions and recessed portions are alternately arranged on a bottom surface of the narrow groove in a cross-sectional view in parallel with a longitudinal direction of the narrow groove. 
     A coating layer is formed on an inner circumference surface of the half member, the coating layer being formed to at least include a region from an inner circumference end to an intermediate portion of an axial direction inner-side surface of the narrow groove. 
     In the present invention, the recessed portions may each be formed to have an arch shape in the cross-sectional view in parallel with the longitudinal direction. 
     Advantageous Effects of Invention 
     The present invention provides the following advantageous effects. 
     The narrow groove is provided without hindering generation of oil film pressure, whereby a friction reducing effect can be achieved with a smaller sliding area and the total quantity of outflow oil can be reduced. With the projecting portions and the recessed portions alternately arranged on the bottom surface of the narrow groove, the lubricant oil is smoothly guided to the inner circumference surface of the half member. Thus, the quantity of sucked back oil can be increased, whereby a friction reducing effect can be obtained and the total quantity of the outflow oil can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a sliding bearing according to an embodiment of the present invention. 
         FIG. 2A  is a plan view of a half member as part of the sliding bearing according to the embodiment of the present invention,  FIG. 2B  is a cross-sectional view of the same taken along line II(B)-II(B), and  FIG. 2C  is a cross-sectional view of the same taken along line  11 (C)- 11 (C). 
         FIG. 3A  is an enlarged cross-sectional view of a narrow groove according to the embodiment of the present invention taken along line II(B)-II(B), and  FIG. 3B  is a partial cross-sectional perspective view of the narrow groove. 
         FIG. 4  is an enlarged cross-sectional view of the narrow groove and a blade according to the embodiment of the present invention taken along line II(B)-II(B). 
         FIG. 5  is a cross-sectional view of a half member according to another embodiment of the present invention taken along line II(C)-II(C). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the invention is described below.  FIG. 1  is a front view of a sliding bearing  1 , with a vertical direction of the sheet defined as an upper and lower direction, and a direction between a closer side and a farther side of the sheet defined as an axial direction (front and rear direction). 
     First of all, half members  2  as parts of the sliding bearing  1  according to an embodiment of the present invention are described with reference to  FIG. 1  and  FIGS. 2A-2C . 
     The sliding bearing  1  is a cylindrical member, and is applied to a sliding bearing structure of a crankshaft  11  of an engine as illustrated in  FIG. 1 . The sliding bearing  1  includes two half members  2  and  2 . The two half members  2  and  2  have shapes obtained by splitting a cylinder in half in a direction parallel with the axial direction, and each have a semicircular cross-sectional shape. In the present embodiment, the half members  2  and  2  are arranged in the upper and lower direction with joining surfaces provided on left and right sides. When the sliding bearing  1  is supporting the crankshaft  11 , a predetermined gap is formed, and lubricant oil is supplied into the gap through an unillustrated oil path. 
       FIG. 2A  illustrates the half members  2  on the upper and the lower sides. In the present embodiment, a rotation direction of the crankshaft  11  corresponds to the clockwise direction in front view as indicated by an arrow in  FIG. 1 . A bearing angle ω is 0° at a right end position in  FIG. 2B , and increases along the counterclockwise direction in  FIG. 2B . More specifically, the bearing angle ω in  FIG. 2B  is defined as 180° at a left end position, and as 270° at a lower end position. 
     The upper half member  2  has an inner circumference provided with a groove extending along a circumference direction and provided with a circular hole at the center. The joining surfaces are provided on the left and right sides of the upper half member  2 . As illustrated in  FIG. 2C , the half members  2  each include a coating layer  23 . 
     The lower half member  2  has an inner circumference with ends in the axial direction provided with narrow grooves  3 . 
     A circumference edge portion  2   a  is formed on a surface on the outer side of each of the narrow grooves  3  in the axial direction, and is formed to have a height h from an outer circumference surface of the half member  2  that is shorter than a height D of a contact surface from an outer circumference surface of the half member  2 . Thus, the circumference edge portion  2   a  on the outer side in the axial direction is formed to be one step lower than the contact surface, adjacent to the circumference edge portion  2   a , to be in contact with the crankshaft  11 . 
     The narrow groove  3  is described with reference to  FIG. 2B  and  FIG. 2C . 
     The narrow grooves  3  are provided on the lower half member  2 . In the present embodiment, two narrow grooves  3  are arranged in parallel in the axial direction. More specifically, the narrow groove  3  extends along the circumference direction to a bearing angle ω 2  in a direction in which the bearing angle ω increases (counterclockwise direction) from a position (with the bearing angle ω of ω 1 ) separated from the joining surface (with the bearing angle ω of 180°) on a downstream side in a rotation direction of the crankshaft  11 . The lower half member  2  has a joining surface on the right side in  FIG. 2B  as a joining surface on an upstream side in the rotation direction, and a joining surface on the left side in  FIG. 2B  as the joining surface on the downstream side in the rotation direction. 
     The narrow groove  3  is formed to have a width was illustrated in  FIG. 2C . 
     The narrow groove  3  is also formed to have a depth d shorter than the height D of the contact surface from the outer circumference surface of the half member  2 . The depth d of the narrow groove  3  changes along a longitudinal direction from one end toward the other end of the narrow groove  3 , as illustrated in  FIG. 3A . 
     As illustrated in  FIG. 3A  as a cross-sectional view taken along line II(B)-II(B) in parallel with the longitudinal direction, projecting portions  3   b  and recessed portions  3   c  are alternately arranged on a bottom surface  3   a  of the narrow groove  3 . 
     The projecting portions  3   b  are each provided between two adjacent recessed portions  3   c  and  3   c . Each projecting portion  3   b  is formed to protrude toward an inner circumference side beyond the recessed portions  3   c.    
     The recessed portions  3   c  each have an arch shape in the cross-sectional view taken along line II(B)-II(B). One recessed portion  3   c  having an arch shape has an end continuing to an end of an adjacent recessed portion  3   c  having the arch shape, and the projecting portion  3   b  is formed as a portion where the recessed portion  3   c  and the recessed portion  3   c  are connected to each other. 
     With the projecting portions  3   b  and the recessed portions  3   c  alternately arranged on the bottom surface  3   a  of the narrow groove  3 , a flow of sucked back lubricant oil as indicated by arrows in  FIG. 3B  can be achieved. Thus, flow of the lubricant oil, flowed into the narrow groove  3 , toward the inner side of the half member  2  in the axial direction by flowing over the side surface of the narrow groove  3  is facilitated. More specifically, the lubricant oil moving along the projecting portion  3   b  from the recessed portion  3   a  creates a flow toward the inner circumference surface side of the half member  2 , so as to be capable of more easily flowing over the side surface of the narrow groove  3 . 
     With this configuration, the quantity of sucked back lubricant oil can be increased, and the total quantity of the outflow oil can be reduced. 
     With the circumference edge portion  2   a  formed one step above a bottom surface  3   a  of the narrow groove  3 , a wall for preventing oil from leaking from a sliding surface to the axial direction end and preventing sucked back oil from leaking again can be provided, whereby a quantity of outflow oil can be reduced. Thus, the quantity of the sucked back oil can be increased during a cold engine operation, and a higher friction reducing effect can be achieved with quick heating. 
     With the circumference edge portion  2   a  formed to be one step lower than the contact surface, adjacent to the circumference edge portion  2   a , to be in contact with the crankshaft  11 , the circumference edge portion  2   a  is less likely to be in contact with the crankshaft  11  inclined to be in a state of being in contact with one end in the axial direction only (partial contact state), and thus can be prevented from being damaged. 
     With the narrow grooves  3  according to the present embodiment, a smaller FMEP is achieved. An especially smaller FMEP is achieved in a region with a low engine speed. The FMEP is a value indicating friction characteristics. Smaller FMEP leads to a lower friction. For example, at the timing of engine cold start, FMEP is reduced and the friction is reduced. 
     Next, a method for forming the narrow groove  3  is described. 
     For example, the narrow groove  3  is formed by cutting. 
     In the cutting, the inner circumference surface of the half member  2  is cut with a blade. In the present embodiment, a circular saw  100  is used as the blade. 
     More specifically, the inner circumference surface of the half member  2  is cut with the circular saw  100  moving in parallel with the longitudinal direction of the narrow groove  3  as illustrated in  FIG. 4 . 
     With the circular saw  100  moving in the manner described above, the recessed portions  3   c  with an arch shape corresponding to an outer circumference (arch shape) of the circular saw  100  are formed on the bottom surface  3   a  of the narrow groove  3 , and the projecting portions  3   b  are each formed between adjacent recessed portions  3   c  and  3   c.    
     The coating layer  23  is coated on the inner circumference surface of the half member  2  to be formed. As illustrated in  FIG. 2C , the coating layer  23  is formed to cover an axial direction inner-side end of the narrow groove  3 . More specifically, the coating layer  23  is formed to an intermediate portion of an axial direction inner-side surface of the narrow groove  3 . With this configuration, the coating layer  23  covering the axial direction inner-side end of the narrow groove  3  can reduce a friction between the inner-side end of the narrow groove  3  in the axial direction and the crankshaft  11  inclined to be in a state of being in contact with one end in the axial direction only (partial contact state). 
     As illustrated in  FIG. 5 , the coating layer  23  may cover the entire narrow groove  3 . With this configuration, a friction between the crankshaft  11  inclined to be in a state of being in contact with one end in the axial direction only (partial contact state) and the axial direction inner-side end and an axial direction outer-side end of the narrow groove  3  can be reduced. 
     As described above, the sliding bearing  1  includes half members  2  and  2 , obtained by splitting a cylinder in half in a direction parallel with an axial direction, arranged on upper and lower sides. The narrow groove  3  extending in the circumference direction is formed on an axial direction end of one of the half members  2  on a lower side, on a downstream side in a rotation direction. The circumference edge portion  2   a  is formed on an outer side of the narrow groove  3  in the axial direction, and is formed to be lower than the contact surface of the sliding bearing  1  to be in contact with the crankshaft  11 . The projecting portions  3   b  and the recessed portions  3   c  are alternately arranged on the bottom surface  3   a  of the narrow groove  3  in a cross-sectional view in parallel with the longitudinal direction of the narrow groove  3 . 
     With the configuration described above, the narrow groove  3  is provided without hindering generation of oil film pressure, whereby a friction reducing effect can be achieved with a smaller sliding area and the total quantity of outflow oil can be reduced. With the projecting portions  3   b  and the recessed portions  3   c  alternately arranged on the bottom surface  3   a  of the narrow groove  3 , the lubricant oil is smoothly guided to the inner circumference surface of the half member  2 . Thus, the quantity of sucked back oil can be increased, whereby a friction reducing effect can be obtained and the total quantity of the outflow oil can be reduced. 
     The recessed portions  3   c  are each formed to have an arch shape in the cross-sectional view in parallel with the longitudinal direction (cross-sectional view taken along line  11 (B)- 11 (B)). 
     With the configuration described above, the lubricant oil can be easily guided toward the inner circumference surface of the half member  2  while moving along the recessed portions  3   c  on the bottom surface  3   a  of the narrow groove  3 , whereby the lubricant oil can be smoothly sent toward the inner side in the axial direction. 
     REFERENCE SIGNS LIST 
     
         
           1  Sliding bearing 
           2  Half member 
           2   a  Circumference edge portion 
           3  Narrow groove 
           3   a  Bottom surface 
           3   b  Projecting portion 
           3   c  Recessed portion 
           11  Crankshaft