Types of Steering Systems Figure shows a simplified pitman-arm type of steering system. The rack-and-pinion type is shown in fig. describes how the wheels are supported on steering knuckles. The steering knuckles are attached to the steering arms by ball joints. The bal joints at each wheel permit the steering knuckle to swing from side to side. This movement turns the front wheels left or right so that the car can be steered. The recirculating ball steering gear is shown in fig. In these units, the worm gear on the end of the steering shaft has a special nut, running on it. The nut rides on rows of small recirculating balls. The recirculation balls move freely through grooves in the worm and inside the nut. As the steering shaft is rotated, the balls force the nut to move up and down the worm gear. A short rack of gear teeth on one side of the nut mesh with the sector gear. Therefore, as the nut moves up and down the worm , the sector gear turns in on direction or the other for steering. The recirculating balls are the only contacts between the worm and the nut. This greatly reduces friction and the turning effort or force applied by the driver for steering. The balls are called recirculating balls because they continuously recirculate from one end of the ball nut to the other end through a pair of ball return guides. For example, suppose the driver makes aright turn, then the worm gear rotated in a clockwise direction when viewed from the drivers seat. This causes the ball nut to move upward. The ball roll between the worm and the ball nut. As the balls reach the upper end of the nut, they enter the return guide and the rollback to the lower end. There they reenter the groove between the worm and the ball nut.
