Internal-gear-type oil pump for vehicle

Abstract

A vehicular internal-gear-type oil pump provided with (a) a circular pump chamber defined by a pump body and a pump cover, (b) an annular driven gear which has internal teeth, and an outer circumferential surface opposed to an inner circumferential surface defining said pump chamber, and which is rotatably supported by the inner circumferential surface defining said pump chamber, and (c) a drive gear which has external teeth engaging with the internal teeth of said driven gear and which is disposed rotatably about an axis of rotation thereof eccentric with respect to an axis of rotation of said driven gear, to rotate said driven gear, characterized in that wherein: said driven gear has a plurality of first dynamic pressure generating grooves formed in local areas of its outer circumferential surface; and each of said first dynamic pressure generating grooves has a depth in a radial direction of the driven gear, which depth is determined such that a gap ratio which is a ratio of a distance of a gap from a bottom of said first dynamic pressure generating groove to said inner circumferential surface to a distance of a gap from the outer circumferential surface of said driven gear to said inner circumferential surface is held within a predetermined range in which a dynamic pressure generated by said first dynamic pressure generating grooves and changing as a function of said gap ratio has a maximal value and in which a fluid friction coefficient generated on the basis of said first dynamic pressure generating grooves and changing as a function of said gap ratio has a minimal value.

1 . A vehicular internal-gear-type oil pump provided with (a) a circular pump chamber defined by a pump body and a pump cover, (b) an annular driven gear which has internal teeth, and an outer circumferential surface opposed to an inner circumferential surface defining said pump chamber, and which is rotatably supported by the inner circumferential surface defining said pump chamber, and (c) a drive gear which has external teeth engaging with the internal teeth of said driven gear and which is disposed rotatably about an axis of rotation thereof eccentric with respect to an axis of rotation of said driven gear, to rotate said driven gear, wherein:
 said driven gear has a plurality of first dynamic pressure generating grooves formed in local areas of its outer circumferential surface; and   each of said first dynamic pressure generating grooves has a depth in a radial direction of the driven gear, which depth is determined such that a gap ratio which is a ratio of a distance of a gap from a bottom of said first dynamic pressure generating groove to said inner circumferential surface to a distance of a gap from the outer circumferential surface of said driven gear to said inner circumferential surface is held within a predetermined range in which a dynamic pressure generated by said first dynamic pressure generating grooves and changing as a function of said gap ratio has a maximal value and in which a fluid friction coefficient generated on the basis of said first dynamic pressure generating grooves and changing as a function of said gap ratio has a minimal value.   
     
     
         2 . The vehicular internal-gear-type oil pump according to  claim 1 , wherein said first dynamic pressure generating groove has a slant surface formed downwardly toward the bottom thereof in the outer circumferential surface of said driven gear, such that said slant surface cooperates with the inner circumferential surface of said pump chamber to define a wedge space. 
     
     
         3 . The vehicular internal-gear-type oil pump according to  claim 1 , wherein said plurality of first dynamic pressure generating grooves are formed in the outer circumferential surface of said driven gear such that the first dynamic pressure generating grooves are equiangularly spaced apart from each other, about the axis of rotation of said driven gear. 
     
     
         4 . The vehicular internal-gear-type oil pump according to  claim 1 , wherein said first dynamic pressure generating grooves have a depth such that said gap ratio is held within a range between 2 and 3. 
     
     
         5 . The vehicular integral-gear-type oil pump according to  claim 1 , wherein said driven gear has a plurality of second dynamic pressure generating grooves formed in local areas of its opposite side surfaces, each of said second dynamic pressure generating grooves having a depth in a thickness direction of the driven gear, which depth is determined such that a gap ratio which is a ratio of a distance of a gap from a bottom of said second dynamic pressure generating groove to inner wall surfaces of said pump chamber, to a distance of a gap from the side surfaces of said driven gear to the inner wall surfaces of said pump chamber is held within a predetermined range in which a dynamic pressure generated by said second dynamic pressure generating grooves has a maximal value and in which a fluid friction coefficient generated on the basis of said second dynamic pressure generating grooves has a minimal value. 
     
     
         6 . The vehicular internal-gear-type oil pump according to  claim 1 , wherein said drive gear has a plurality of third dynamic pressure generating grooves formed in local areas of its opposite side surfaces, each of said third dynamic pressure generating grooves having a depth in a thickness direction of the drive gear, which depth is determined such that a gap ratio which is a ratio of a distance of a gap from a bottom of said third dynamic pressure generating groove to inner wall surfaces of said pump chamber, to a distance of a gap from the side surfaces of said drive gear to the inner wall surfaces of said pump chamber is held within a predetermined range in which a dynamic pressure generated by said third dynamic pressure generating grooves has a maximal value and in which a fluid friction coefficient generated on the basis of said third dynamic pressure generating grooves has a minimal value.