Vibration control system

A variable damper comprising;

• an outer member including a magnetically conductive sleeve;
• an inner member comprising a shaft;
• and
• an electromagnet supported between the members;
• wherein:
• a chamber formed between the outer and inner members is at least partially filled with magnetorheological fluid (MRF), such that when a magnetic field is applied to the chamber, the effective viscosity of the fluid increases such that relative motion of the inner and outer members is opposed;
• and
• characterized in that the electromagnet is supported in the chamber to provide a first fluid flow path between the outer member and electromagnet, and a second fluid flow path between the inner member and the electromagnet, the region between the electromagnet and the magnetically conductive sleeve defining a control region in the first fluid flow path in which the magnetic field is concentrated.

A method of variably damping relative motion between an outer member including a magnetically conductive sleeve and an inner member, comprising the steps:

• (a) supporting an electromagnet between the members, such that a first flow path exists between the electromagnet and the sleeve, and a second flow path exists between the electromagnet and the inner member;
• (b) placing a magnetorheological fluid between the members;
• (c) applying a minimal magnetic field to the electromagnet;
• (d) increasing the magnetic field in the first flow path;
• and
• (e) increasing viscosity of the fluid to thereby oppose relative motion of the members and create damping with minimal off-state.

A vibration control system for reducing vibrations comprising:

• a first and a second element;
• and
• a variable damper, located between the first and second elements, including an outer member including a magnetically conductive sleeve;
• an inner member comprising a shaft;
• and an electromagnet supported between the members, wherein a chamber formed between the outer and inner members is at least partially filled with magnetorheological fluid (MRF), such that when a magnetic field is applied to the chamber, the effective viscosity of the fluid increases such that relative motion of the inner and outer members is opposed and characterized in that the electromagnet is supported in the chamber to provide a first fluid flow path between the outer member and electromagnet, and a second fluid flow path between the inner member and the electromagnet, the region between the electromagnet and the magnetically conductive sleeve defining a control region in the first fluid flow path in which the magnetic field is concentrated, wherein the vibration control system causes active damping between the elements such that a relative figure of merit of less than 0.83.