Variable stiffness bushing

A variable stiffness bushing, comprising:

• an inner tubular member arranged along an axis;
• an outer tubular member disposed coaxially around the inner tubular member with a prescribed gap defined between the outer tubular member and the inner tubular member;
• a tubular elastic member connecting the inner tubular member and the outer tubular member;
• at least one pair of liquid chambers defined in the elastic member such that the liquid chambers are circumferentially separated from one another and first axial ends and second axial ends of the liquid chambers are defined by a first end wall and a second end wall of the elastic member, respectively;
• at least one communication passage each including a circumferential passage provided in the outer tubular member and extending in a circumferential direction, each of the at least one communication passage communicating the liquid chambers of a corresponding pair of the at least one pair of liquid chambers with each other;
• a magnetic fluid filling the at least one pair of liquid chambers and the at least one communication passage,
• wherein the first end wall and the second end wall are configured such that when the inner tubular member and the outer tubular member are axially displaced relative to each other, a difference is created between volumes of the liquid chambers of each pair of the at least one pair of liquid chambers,
• wherein when a vertical direction is defined as a direction of the axis of the inner tubular member, the outer tubular member includes a cylindrical inner yoke disposed along the axis, a coil coaxially wound around the inner yoke, an outer yoke surrounding the coil, a tubular lower yoke jointed to a lower end of the outer yoke and opposing a lower end of the inner yoke via a gap so that at least one annular gap each constituting the circumferential passage of a corresponding one of the at least one communication passage is formed on an inner side of the coil, and a tubular passage forming member made of a non-magnetic material and positioned between the inner yoke and the elastic member, the tubular passage forming member closing the at least one annular gap such that the circumferential passage of each communication passage is defined between the tubular passage forming member and the coil,
• wherein the tubular passage forming member is formed with at least one pair of communication holes, each pair of the at least one pair of communication holes communicating the circumferential passage of a corresponding one of the at least one communication passage with a corresponding pair of the at least one pair of liquid chambers, and
• wherein when an electric current flowing through the coil generates a magnetic field around the coil, the inner yoke, the outer yoke, and the lower yoke of the outer tubular member jointly form a magnetic circuit.