Method for producing cylindrical bushing with hydraulic damping

A method for producing a cylindrical bushing with hydraulic damping, which has an outer cylinder, a cylindrical internal ring press-fitted into said outer cylinder, a vibration-damping rubber block disposed within said internal ring, and an inner cylinder coaxially embedded in said rubber block, said rubber block having a main portion which horizontally extends and is joined to an inner periphery of said internal ring at horizontally opposed peripheral surfaces thereof, and wall portions which radially upwardly extend from both axial ends of said main portion and are joined to said inner periphery of said internal ring at peripheral surfaces thereof, an axially central portion of said internal ring being inwardly caved, a throttling member having a throttle passageway being disposed between said inwardly caved central portion of said internal ring and said outer cylinder, a thin diaphragm being disposed between a lower surface of said rubber block and said outer cylinder to define an auxiliary liquid chamber, and said auxiliary liquid chamber communicating with said main liquid chamber by way of said throttle passageway, comprising the steps of:

• preparing an internal ring having an elliptical cross-section including a major axis and a minor axis;
• disposing said vibration-damping rubber block within said internal ring so that said main portion extends along said major axis thereof and said wall portions extend along said minor axis thereof;
• deforming said internal ring so as to have a circular cross-section;
• and
• press-fitting said deformed internal ring into said outer cylinder with said throttling member interposed between said inwardly caved central portion of said internal ring and said outer cylinder, and said thin diaphragm disposed between said lower surface of said rubber block and said outer cylinder.