Recirculating Ball Steering System

     A recirculating ball steering system appears mainly on lorries and some SUVs. Themain difference to a rack-and-pinion system is the use of a worm gear. A worm gear has arevolving cylinder with a screw-like thread. It is a steering mechanism in which thesteering shaft turns a worm gear that，in turn, causes a toothed metal block to move backand forth. Ball bearings in a recirculating track reduce friction between the worm gear andthe block. As the block moves, its teeth rotate a gear connected to a steering arm, whichthen moves the steering linkage.

    The driver turns the steering wheel. This movement revolves the worm gear. Theworm gear then causes a block to move a serrated gear. The gear moves a piece of metalrod called a pitman arm. the pitman arm connects to a track rod. In a similar fashion torack-and-pinion steering，the track rod has tie rods at each end. These connect to thewheels' steering arms. The name "recirculating ball" comes from the ball bearings that are in theblock that the worm gear turns. The ball bearings recirculate around the inside of the block.

    The primary components of the recirculating ball steering system are：pitman armshaft，idler arm, track rod or center link，tie-rod, tie-rod end and adjustment sleeve.