Magnetorheological devices with permanent magnet field bias

A magneto-rheological damping device comprises a piston and a case element, both capable of acting to carry a magnetic flux. A passage exists between the piston and the case element, and an amount of MR fluid is positioned between the piston and the case element to flow within the passage. A first magnetic flux generator and a second magnetic flux generator cooperate to generate a net flux that is disposed to act upon the MR fluid in the passage to affect the flow of fluid in the passage. One of the flux generators comprises a permanent magnet to generate a bias flux between the piston and the case element, and the other flux generator comprises a means for providing a controllable magnetic flux between the piston and the case element.