Abstract: A method for manufacturing a coiled spring having a high fatigue strength to be used for example as a suspension spring of a car using a rod of tensile strength 1910 to 2020 N/mm2 and diameter 8 to 17 mm. In a cold coiling step, the rod is formed into a coil. Annealing is then carried out to remove strains having arisen inside the coil during the coiling step. A hot setting step of utilizing surplus heat from the annealing step and applying a predetermined load to the coil to compress it for a predetermined time is then carried out. After that, multi-stage shot peening is carried out on the coil.

Abstract: A hydraulic damper has a first oil chamber, a second oil chamber, a communication mechanism defining a communication oil passage, the first and second oil chambers communicating with each other through the communication oil passage, and a damping force adjusting mechanism for varying a cross-sectional area of the communication oil passage to adjust damping forces. The damping force adjusting mechanism includes an adjusting rod having an end disposed in a portion of the communication oil passage, the adjusting rod being movable toward and away from the communication oil passage to vary the cross-sectional area of the communication oil passage, an eccentric cam rotatably disposed in engagement with an opposite end of the adjusting rod, and a rotary actuator for rotating the eccentric cam to move the adjusting rod toward and away from the communication oil passage to adjust the damping forces.