Magnetorheological fluid damper tunable for smooth transitions

A damper, comprising:

• a cylinder containing a magnetorheological fluid;
• and
• a piston assembly slidably mounted for reciprocal movement in the cylinder to form a first chamber positioned on one side of the piston assembly and a second chamber positioned on an opposite side of the piston assembly, the piston assembly having a fluid flow passage therethrough defining a flow gap permitting limited fluid flow between the first chamber and the second chamber, wherein the flow gap comprises an annular, axially directed passage within the piston assembly, and at least first and second grooves adjacent and open to the flow gap along at least a portion of the flow gap in the direction of fluid flow, and the first groove is axially directed along one of an inner wall and an outer wall defining the annular, axially directed passage and the second groove is axially directed along the other of an inner wall and an outer wall defining the annular, axially directed passage, the piston assembly further including a magnet assembly establishing a magnetic flux circuit through the flow gap and through the grooves in series with a region of the flow gap adjacent the grooves, the magnetic flux being established through the flow gap and grooves transversely to the direction of fluid flow therethrough to cause magnetorheological fluid flowing through the flow gap and the grooves to experience a magnetorheological effect affecting the flow of the magnetorheological fluid therethrough, whereby the grooves causes the magnetic flux density therethrough to be smoothly reduced from that in the remainder of the flow gap.