Patent ID: 8071003

Claim:
A method of manufacturing a vibration damping bushing including (i) a main shaft member, (ii) a rubber elastic body of tubular shape affixed to an outside peripheral face of the main shaft member, and (iii) a medial sleeve of tubular shape embedded coaxially in a medial region of the rubber elastic body in a thickness-wise direction thereof, the method comprising the steps of: (A) employing a mold assembly composed of an upper mold and a lower mold positioned spaced a distance apart in a vertical direction, and an intermediate mold to form a tubular cavity defining face extending about a center axis vertically extending between the upper and lower molds, said intermediate mold being split a plurality of sections in a circumferential direction of the cavity defining face, with each of the plurality of sections movable forward and backward in a centripetal direction between the upper and lower molds; (B) after setting in the mold assembly the main shaft member and the medial sleeve so as to be positioned coaxially with each center axis extending in the vertical direction between the upper and lower molds, filling a mold cavity of the mold assembly with a rubber material and then the rubber material is vulcanized so that the rubber elastic body is simultaneously bonded to the main shaft member and the medial sleeve, wherein: after setting the main shaft member on the lower mold so as to project vertically upward while positioning a lower end of the main shaft member with respect to the lower mold, the medial sleeve is set so as to be disposed about the main shaft member, and the plurality of sections are moved forward in the centripetal direction from an outer peripheral side to form the intermediate mold together, and then the upper mold is superposed onto the intermediate mold from a vertically upper side to form the mold cavity therein, at least one positioning protrusion is formed on the cavity defining face, the positioning protrusion being discontinuous in the circumferential direction, while being located at either semi-circumference of the cavity defining face with any diametric line interposed therebetween, and the medial sleeve is set in position in an axis-perpendicular direction within the mold cavity by holding the positioning protrusions in contact against an outer peripheral face of the medial sleeve, the positioning protrusions are positioned only on an axially upper side of an axially central portion of the cavity defining face so that the positioning protrusions are adapted to hold an upper end position of the medial sleeve, and only the lower mold of the mold assembly is furnished with a positioning portion for positioning a lower end portion of the medial sleeve, the positioning portion has a form of rectangular cross-sectional slot discontinuous in a circumferential direction.