Worm and Roller
The worm and rotter steering gea is quite similar to the worm and sector, except a roller is supported by ball or rotter bearings within the sector mounted on the pitman arm shaft. These bearings assist in reducing sliding friction between the worm and sector. As the steering wheel turns the worm, the roller turns with it, forcing the sector and pitman arm shaft to rotate.
The hourglass shape of the worm, which tapers from both ends to the center, affords better contact between the worm and roller in all positions. This design provides a variable steering ratio to permit faster and more efficient steering.
"Variable steering ratio" means that the ratio is larger at one position than another. Therefore the wheels are turned faster at certain positions than at others. At the center or straight-ahead position, the steering gear ratio is high, giving more steering control. However, as the wheels are turned, the ratio decreases so that the steering action is much more rapid. This design is very helpful for parking and maneuvering the vehicle.
Cam and Lever
The cam and lever steering gear. in which the worm is known as a cam and the sector as the lever. The lever carries two studs that are mounted in bearings and engage the cam. As the steering wheel is turned, the studs move up and down on the cam. This action causes the lever and pitman arm shaft to rotate. The lever moves more rapidly as it nears either end of the cam. This action is caused by the increased angle of the lever in relation to the cam. Like the worm and roller, this design allows for variable steering ratio.
Worm and Nut
The worm and nut steering gear is made in several different combinations. A nut is meshed with and screws up and down on the worm gear. The nut may operate the pitman arm directly through a lever or through a sector on the pitman arm shaft.
The recirculating ball is the most common type of worm and nut steering gear . In this steering gear, the nut, which is in the form of a sleeve block, is mounted on a continuous row of balls on the worm gear to reduce friction. Grooves are cut into the ball nut to match the shape of the worm gear. The ball nut is fitted with tubular ball guides to return the balls diagonally across the nut to recirculate them, as the nut moves up
Worm and nut steering gear (recirculating ball type).
and down on the worm gear. With this design, the nut is moved on the worm gear by rolling instead of sliding contact. Turning the worm gear moves the nut and forces the sector and pitman arm shaft to turn.
Rack and Pinion
The rack-and-pinion steering gear has become increasingly popular on smaller passenger vehicles. It is simpler, more direct acting, and may be straight mechanical or power-assisted.
The manual rack-and-pinion steering gear basically consists of a steering gear shaft, pinion gear, rack. thrust spring, bearings, seals, and gear housing. In the rack-and-pinion steering system the end of the steering gear shaft contains a pinion gear, which meshes with a long rack. The rack is connected to the steering arms by tie rods, which are adjustable for maintaining proper toe angle. The thrust spring preloads the rack-and-pinion gear teeth to prevent excessive gear backlash. Thrust spring tension may be adjusted by using shims or an adjusting screw.