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1. EP1983214 - FLUID DAMPER

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[ EN ]
Claims

1. A fluid damper comprising: a fluid having magnetic properties, a piston formed of a magnetic material; a cylinder which encapsulates the fluid having magnetic properties and accommodates the piston; a piston rod which pierces an end face member of the cylinder in an axial direction to support the piston; a magnetic field generation device provided outside the cylinder; a first yoke which is arranged around the cylinder and magnetically connects the piston with the magnetic field generation device; and a second yoke which is arranged around the piston rod outside the cylinder and magnetically connects the piston rod with the magnetic field generation device, wherein the piston rod has: a magnetic portion which forms a first magnetic circuit together with the piston, the first yoke, the magnetic field generation device, and the second yoke when the piston is displaced to one side in the axial direction beyond a neutral region; a magnetic portion which forms a second magnetic circuit together with the piston, the first yoke, the magnetic field generation device, and the second yoke when the piston is displaced to the other side in the axial direction beyond the neutral region; and a non-magnetic portion which cuts off the first magnetic circuit and the second magnetic circuit when the piston is in the neutral region, and a magnetic flux density of each magnetic circuit passing through a gap between an outer peripheral surface of the piston and an inner peripheral surface of the cylinder varies in accordance with movement of the piston in the axial direction.
  2. The fluid damper according to claim 1, wherein the piston formed of a magnetic material is constituted of at least a pair of first and second pistons formed of a magnetic material which are arranged to face each other through a non-magnetic material with a gap therebetween in the axial direction, and the first and second pistons formed of a magnetic material have bypasses allowing the fluid having magnetic properties to flow therethrough only in directions opposite to each other.
  3. The fluid damper according to claim 2, wherein a cylinder chamber of the cylinder is partitioned by the pair of pistons into a first cylinder chamber, a second cylinder chamber, and a third cylinder chamber sandwiched between the pair of pistons, the first piston on the first cylinder chamber side includes a valve which allows the fluid having magnetic properties to flow only in a direction from the first cylinder chamber to the third cylinder chamber at the bypass allowing the first cylinder chamber to communicate with the third cylinder chamber, the second piston on the second cylinder chamber side includes a valve which allows the fluid having magnetic properties to flow only in a direction from the second cylinder chamber to the third cylinder chamber at the bypass allowing the second cylinder chamber to communicate with the third cylinder chamber, and the piston rod has: a magnetic portion which forms a first magnetic circuit together with the first piston, the first yoke, the magnetic field generation device, and the second yoke when the first piston is displaced toward the first cylinder chamber side beyond a neutral region; a magnetic portion which forms a second magnetic circuit together with the second piston, the first yoke, the magnetic field generation device, and the second yoke when the second piston is displaced toward the second cylinder chamber side beyond the neutral region; and a non-magnetic portion which cuts off the first magnetic circuit when the first piston is in the neutral region and cuts off the second magnetic circuit when the second piston is in the neutral region.
  4. The fluid damper according to claim 2, wherein a cylinder chamber of the cylinder is partitioned by the pair of pistons into a first cylinder chamber, a second cylinder chamber, and a third cylinder chamber sandwiched between the pair of pistons, the first piston on the first cylinder chamber side includes a valve which allows the fluid having magnetic properties to flow only in a direction from the third cylinder chamber to the first cylinder chamber at the bypass allowing the first cylinder chamber to communicate with the third cylinder chamber, the second piston on the second cylinder chamber side includes a valve which allows the fluid having magnetic properties to flow only in a direction from the third cylinder chamber to the second cylinder chamber at the bypass allowing the second cylinder chamber to communicate with the third cylinder chamber, and the piston rod has: a magnetic portion which forms a first magnetic circuit together with the first piston, the first yoke, the magnetic field generation device, and the second yoke when the first piston is displaced toward the first cylinder chamber side beyond a neutral region; a magnetic portion which forms a second magnetic circuit together with the second piston, the first yoke, the magnetic field generation device, and the second yoke when the second piston is displaced toward the second cylinder chamber side beyond the neutral region; and a non-magnetic portion which cuts off the first magnetic circuit when the first piston is in the neutral region and cuts off the second magnetic circuit when the second piston is in the neutral region.
  5. The fluid damper according to claim 1, wherein a magneto-rheological fluid is used as the fluid having magnetic properties.
  6. The fluid damper according to claim 1, wherein a magnetic fluid is used as the fluid having magnetic properties.
  7. The fluid damper according to claim 1, wherein a permanent magnet is used as the magnetic generation device.
  8. The fluid damper according to claim 1, wherein a solenoid is used as the magnetic field generation device.